2012-039
2013
research-articleArticleXXX10.1144/petgeo2012-039N. E. Holgate et al.Krossfjord and Fensfjord formations, Troll Field
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
Sedimentology and sequence stratigraphy of the Middle–Upper Jurassic
Krossfjord and Fensfjord formations, Troll Field, northern North Sea
Nicholas E. Holgate1,*, Christopher A.-L. Jackson1, Gary J. Hampson1 and Tom Dreyer2
1Department
of Earth Science & Engineering, Imperial College, London SW7 2BP, UK
UK Ltd, One Kingdom Street, Paddington, London W2 6BD, UK
*Corresponding author (e-mail: [email protected])
2Statoil
ABSTRACT: The Middle–Upper Jurassic Krossfjord and Fensfjord formations are secondary reservoir targets in the super-giant Troll oil and gas
field, Horda Platform, offshore Norway. The formations comprise sandstones
(c. 195 m thick) sourced from the Norwegian mainland to the east, that pinch
out basinwards into offshore shales of the Heather Formation to the west. Sedimentological analysis of cores from the Troll Field has identified six facies
associations, which represent wave- and tide-dominated deltaic, shoreline and
shelf depositional environments. Resulting depositional models highlight the
complex distribution of depositional environments, and reflect spatial and temporal variations in physical processes at the shoreline, rate of sediment supply
and accommodation development. These models are further complicated by the
absence of coastal plain facies, which implies that the Troll Field was fully
subaqueous during deposition, that shoreline regression was forced by falling
sea level or that coastal plain deposits were removed by transgression. Genetic
sequences bounded by major flooding surfaces (‘series’) exhibit laterally uniform thicknesses, implying no major tectonic influence on sedimentation. The
recognition of pronounced variability in facies character and stratigraphical
architecture emphasize the need for a robust depositional model of the formations in order to drive future exploration in these, and coeval, reservoirs.
INTRODUCTION
The super-giant Troll oil and gas field is located on the Horda
Platform on the eastern margin of the Viking Graben, northern
North Sea (Fig. 1a), and has produced 220.7 million Sm3
(1.39 billion barrels) of oil and 391.8 billion Sm3 (13.84 trillion
cubic feet) of gas during 21 years of production since 1990
(NPD 2011). The Troll Field is divided into the Troll West and
Troll East accumulations, although pressure communication has
been proven between the two accumulations (NPD 2011).
Rotated fault blocks define the traps for both accumulations
(Fig. 1c) and the reservoir consists of shallow-marine sandstones; production to date has been from the Sognefjord
Formation (Oxfordian–Kimmeridgian/Volgian) (Fig. 2). The
underlying Fensfjord Formation (Callovian) forms part of the
reservoir and has a proven oil column of 6–9 m in the northern
part of Troll East (NPD 2011). The Fensfjord Formation also
forms a significant reservoir in the Brage Field (Callovian–
Oxfordian), which lies 20 km to the SW of Troll (Fig. 1a). The
Sognefjord and Fensfjord formations, together with the underlying Krossfjord Formation (Bathonian), form part of the
Viking Group, which is situated above the prolific Brent Group
(Fig. 2).
The sedimentology of the Krossfjord and Fensfjord formations is poorly understood as they have not been the focus of
previous published work, despite the formations containing
potentially large reserves. The formations comprise sandstones
Petroleum Geoscience, Vol. 19, 2013, pp. 237–258
doi: 10.1144/petgeo2012-039
Published Online First on May, 02, 2013
principally sourced from the Norwegian mainland to the east
and pinch out basinwards into the offshore shales of the Heather
Formation to the west towards the North Viking Graben (Stewart
et al. 1995). The development of a detailed sedimentological
and sequence stratigraphical model for the Krossfjord and
Fensfjord formations is complicated by two factors. First, the
sedimentological character, distribution and stratigraphical architecture of shallow-marine sandstones are strongly controlled by
spatial and temporal variation in physical processes at and near
the shoreline (e.g. wave- v. tide- v. fluvial-dominated processes)
(e.g. Gani & Bhattacharya 2007; Ainsworth et al. 2011). Second,
the geographical partitioning and the relative importance of
physical processes can be further complicated in rifts due to
fault-block rotation, uplift and subsidence; the sedimentology
and stratigraphical architecture of both the Krossfjord and
Fensfjord formations may, thus, be anticipated to be complex
because they were deposited during the Middle–Late Jurassic rift
event (Ravnås & Bondevik 1997).
The aims of this paper are twofold: (1) to produce a highresolution sedimentological and sequence stratigraphical model
for the Krossfjord and Fensfjord formations in the Troll Field;
and (2) to determine the dominant shoreline processes and
genetic stratigraphical relationships within and between these
formations. The work reported herein will improve our understanding of syn-rift sandstone distribution in the northern North
Sea, and guide future exploration and production from
Krossfjord and Fensfjord reservoirs.
© 2013 EAGE/The Geological Society of London
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Fig. 1. (a) Simplified map of the north Viking Graben highlighting the Horda Platform, and the Troll, Brage, Fram and Gjøa fields, which host
Krossfjord and Fensfjord reservoirs (modified after Færseth 1996; Ravnås & Bondevik 1997; Fraser et al. 2002). (b) Simplified palaeoenvironmental
map of the northern North Sea during the mid- to late Callovian and deposition of the Fensfjord Formation in the Troll Field (modified after Husmo
et al. 2002). (c) Geoseismic profile illustrating the major fault blocks from west to east across the Viking Graben (modified after Husmo et al. 2002).
Cross-sections (c and Fig. 2) and maps (Fig. 3) are located in (a).
GEOLOGICAL SETTING AND PREVIOUS
WORK
Regional tectonic context
The Troll Field is located on the Horda Platform, on the eastern
flank of the North Viking Graben. The northern part of the
North Sea rift basin is a fault-bounded depocentre that is
170–200 km wide, and is flanked by the Shetland Platform to
the west and the Norwegian mainland to the east. It is the northern arm of the North Sea trilete rift system, which was initially
developed during the Triassic as a continental rift system, and
was reactivated and significantly expanded during the Late
Jurassic as a marine rift system (Roberts et al. 1990a; Davies
et al. 2001). It is characterized by normal faults that strike north,
NE or NW, and which bound rotated fault blocks that are
15–50 km wide (Færseth & Ravnås 1998). The fault blocks are
arranged around a central low, known as the Viking Graben
(Færseth & Ravnås 1998). The North Viking Graben is located
in the North Sea between 59o and 61ºN, and represents one arm
of the trilete failed rift system (Fig. 1a).
The basin underwent a complex tectonic evolution; initial
phase of extension occurred during the Permo-Triassic, and multiple phases of extension occurred in the Middle–Late Jurassic
(Bajocian–Volgian). The Permo-Triassic and Middle–Late Jurassic
phases of rifting are separated by a post-rift interval, in which
two regional tectonic uplift events are identified in the
Hettangian and late Toarcian–Aalenian (Steel 1993; Færseth
1996; Færseth & Ravnås 1998). During the Early Jurassic the
basin was characterized by tectonic quiescence and spatially uniform subsidence. The Toarcian–Aalenian event interrupted this
period of quiescence and formed the North Sea thermal dome,
which provided clastic sediment for the northwards progradation
and subsequent southwards retreat of the Middle Jurassic ‘Brent
Delta’ (Ziegler 1990; Underhill & Partington 1993). The subsequent Middle–Late Jurassic depositional systems, rather than
being sourced from the North Sea dome, were sourced from the
Norwegian mainland to the east and prograded to the west.
These systems were deposited across a series of north–southtrending fault blocks that formed during the Middle–Late
Jurassic rift event (Rattey & Hayward 1993).
The trilete Middle–Late Jurassic rift system formed in
response to the deflation of the North Sea thermal dome (Ziegler
1990; Underhill & Partington 1993). Both the initiation and cessation of rifting was diachronous across the basin; in the northern North Sea, rifting initiated in the Bajocian (Johannessen
et al. 1995; Hesthammer et al. 1999). The rate of extension and
fault-controlled subsidence generally increased through the
Jurassic, and were greatest in the Late Oxfordian–Kimmeridgian
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
Krossfjord and Fensfjord formations, Troll Field
Stage
Valanginian
Ryazanian
Ma
Viking
Graben
128
West
Upper
Jurassic
Brage
Horst
Horda PlaŽorm
East
131
Draupne Fm
Volgian
Kimmeridgian
Oseberg
Fault Block
140
Heather “C” unit
145
Sognešord Fm
Oxfordian
152
MFS
157
MFS
Bathonian
Bajocian/Aalenian
KEY
MFS
Heather “B” unit
Fensšord Fm
Heather “A” unit
Krossšord Fm
Tarbert Fm
165
Ness Fm
Angular unconformity
Shallow marine sandstones
Maximum flooding surface
Siltstones
2nd order sequence
Claystones
(Færseth & Ravnås 1998). However, in detail, the Middle–Late
Jurassic rift event can be divided into several discrete phases of
basin-wide rifting and fault-related subsidence; these phases are
discussed further below, so that our detailed sedimentological
and stratigraphical analysis can be placed in a robust, regional,
tectonostratigraphical framework.
Tectonic–stratigraphical evolution of Horda
Platform and Troll Field
The Troll Field and surrounding area contains three major sandstone tongues of Middle–Late Jurassic age. These are the
Krossfjord, Fensfjord and Sognefjord formations of the Viking
Group (Vollset & Doré 1984) (Fig. 2), which are each 100–200 m
thick near the rift margin and which pinch-out westwards into
fine-grained Heather Formation deposits in the North Viking
Graben (Ravnås & Bondevik 1997). The sandstone tongues were
deposited in several transgressive–regressive cycles at the margins of a shallow sea that covered the Horda Platform (Stewart
et al. 1995). The combined thickness of the sandstone tongues,
and associated Heather Formation siltstones and mudstones, is up
to 400 m (Husmo et al. 2002). The Heather Formation is informally split into three parts on the Horda Platform to describe its
stratigraphical relationship to the three major sandstone tongues:
the Heather ‘A’ unit lies above the Brent Group and beneath the
Krossfjord Formation (Bathonian); the Heather ‘B’ unit overlies
the Fensfjord Formation and underlies the Sognefjord Formation
(Callovian); and the Heather ‘C’ unit overlies the Sognefjord
Formation (Oxfordian and Kimmeridgian) (Stewart et al. 1995).
The Sognefjord Formation is locally directly overlain by the
Draupne Formation and the Heather ‘C’ unit is absent; in these
locations the contact between the Sognefjord and Draupne formations is an angular unconformity (Stewart et al. 1995).
Deposition of the Krossfjord, Fensfjord and Sognefjord formations was driven by the supply of coarse clastic material from
the eastern flank of the developing North Sea rift system as a
result of uplift of the Norwegian hinterland (Stewart et al. 1995;
Ravnås & Bondevik 1997). Each of the three formations has
been interpreted as a second-order genetic sequence (sensu
Brent
Gp
Middle
Callovian
Viking Group
Age
239
Fig. 2. Middle–Upper Jurassic
chronostratigraphical framework for a SW–
NE-orientated cross-section through the
North Viking Graben and Horda Platform
(Fig. 1a) (modified after Partington et al.
1993; Stewart et al. 1995; Fraser et al.
2002).
Galloway 1989), which is bounded by major flooding surfaces
(Fig. 2) (Stewart et al. 1995). Deposition in a range of shelf-toshoreface environments, with varying degrees of tidal and/or fluvial influence, has been interpreted for the formations (Ravnås
& Bondevik 1997; Dreyer et al. 2005).
The tectonostratigraphical evolution of the Horda Platform
and the North Sea rift system resulted in the development of
three structural provinces: (1) the relatively stable Horda
Platform in the east; (2) a number of tilted half grabens that host
the Brage, Oseberg, Troll and Fram fields (Stewart et al. 1995);
and (3) the deep, fault-bounded, North Viking Graben in the
west (Fig. 1). Rifting during the Middle–Late Jurassic can be
subdivided into three periods (Fig. 2) (Fraser et al. 2002).
(i) Bathonian–latest Callovian. During the initial Bathonian–
latest Callovian period of rifting, a series of faulted terraces
developed between the Viking Graben and the Horda Platform. Rotation of the normal fault blocks, which define the
traps of the Oseberg and Brage fields, caused local reworking of the upper Ness and Tarbert formations (Brent Group)
on the Horda Platform (Husmo et al. 2002). It was during
this period of rifting that the Krossfjord and Fensfjord formations were deposited (Vollset & Doré 1984; Steel 1993).
In the Troll Field, the Krossfjord Formation is characterized
by progradation of a sand-rich delta during relatively low
rates of normal faulting and fault-block rotation (Ravnås
et al. 2000) (Fig. 2). The Fensfjord Formation consists of
regressively stacked, fine-grained sandstones, which accumulated during a period of tectonic quiescence during the
Middle Callovian, when the sediment supply rate was higher
than the basin subsidence rate (Steel 1993; Stewart et al.
1995; Ravnås & Bondevik 1997; Fraser et al. 2002). At the
point of maximum regression during the Late Callovian,
the Fensfjord Delta covered the entire Horda Platform and
extended into the distal sub-basins that now host the Brage
and Oseberg fields (Fig. 2) (Husmo et al. 2002). It has been
speculated that turbidites, which were presumably sourced
from the collapse of the Fensfjord Delta front, were deposited westwards of the Fensfjord Delta at this time (Ravnås
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240
N. E. Holgate et al.
et al. 2000). Landwards migration of the Fensfjord Delta
is attributed to fault-related subsidence outpacing sediment
supply, which was coeval with footwall uplift of the western and NW boundary faults of the Horda Platform. Faultcontrolled uplift in the Brage area resulted in the creation
of footwall islands, which represented an important intrabasinal sediment source (Ravnås et al. 2000; Husmo et al.
2002). A marine transgression occurred in the Late Callovian
and resulted in deposition of fine-grained sediments of the
Heather ‘B’ unit (Steel 1993).
(ii) Oxfordian–Kimmeridgian. During this period the Sognefjord Formation was deposited and rifting reached its climax,
creating the major structural divide between the Viking Graben and the Horda Platform (Stewart et al. 1995). Increased
extension caused uplift and tilting of fault blocks, resulting
in fault-block footwalls rising above sea level at the margins
of the Horda Platform. Erosion occurred on these footwall
crests, allowing older sediment of the Sognefjord Formation
to be reworked and deposited (Fraser et al. 2002).
(iii) Early–Middle Volgian. The final stage of rifting caused
extensive faulting in the west of the Viking Graben and mild
reactivation of faults on the Horda Platform; this resulted in
uplift and eastwards tilting of normal fault blocks (Fossen
et al. 2003). Consequently, many fault blocks suffered local
erosion and collapse, which resulted in Lower and Middle
Jurassic strata being truncated beneath Upper Jurassic strata in
several locations on the Horda Platform (Husmo et al. 2002).
Deposition of the Sognefjord Formation was terminated by
marine flooding, which led to deposition of deep-marine mudstones of the Draupne Formation (Fraser et al. 2002).
Previous depositional models for the Viking Group
Several depositional models have been published for the sandstones of the Viking Group, with a particular focus on the
Sognefjord Formation. An early model interpreted the Sognefjord
Formation sandstones as offshore bars, and proposed that transgressive erosion was the main control on facies distribution
(Whitaker 1984; Hellem et al. 1986; Osborne & Evans 1987).
Eustatic sea-level rise was interpreted to have been the major
controlling factor on sedimentation. Subsequent models interpreted the sandstone tongues of the Viking Group to represent
regressive–transgressive deltaic units containing a variety of
shallow-marine shelf to shoreface environments (e.g. Steel 1993;
Stewart et al. 1995). A greater tectonic influence on sedimentation was also suggested due to the recognition of variations in
stratal thickness identified on seismic reflection data. The most
recent model for the Oxfordian part of the Sognefjord Formation
interprets the delta to have been mixed influence, with a wavedominated spit deflecting fluvially supplied sediment towards
the SW (Dreyer et al. 2005). The spit is interpreted to have been
attached to the coast in the north and bordered to the east by a
tidal backbasin. These various depositional models have different implications for predicted facies distributions across the
Troll Field and elsewhere on the Horda Platform and North
Viking Graben.
DATASET
Thirty-two wells in the Troll Field penetrate the Fensfjord
Formation, and 22 of these wells also penetrate the underlying
Krossfjord Formation (NPD 2011). Nine of these wells contain
core within the interval of interest, giving a total core length of
893 m, all of which has been logged at a scale of 1:50 (Fig. 3,
Table 1). In most wells, only the upper part of the Fensfjord
Formation is cored. Only one well, 31/2-4R, has complete core
recovery of the Fensfjord Formation. Wells 31/5-5 and 31/2-4R
have partial core recovery from the Krossfjord Formation (Table
1). Sedimentological facies analysis included describing grain
size and shape, sorting, sedimentary structures, diagenetic features and the nature of bedding contacts. In addition, trace and
body fossils were documented, including their orientation, size,
cross-cutting relationships and intensity of bioturbation (cf.
Bockelie & Howard 1984; MacEachern & Bann 2008). A
biostratigraphical framework for the Fensfjord Formation was
established by Whitaker (1984) in the Brage Field. This framework has recently been extended to five cored wells in the Troll
Field, through analysis of quantitative palynology and kerogen
counts (GeoStrat 2011). Wireline-log data have been used to
identify facies in uncored wells. Borehole image and dipmeter
data are not available for the studied wells, thus palaeocurrent
directions could not be reconstructed from cored or uncored section of the wells.
Two regional three-dimensional (3D) seismic reflection data
sets that cover the Troll Field have been interpreted (North Sea
exploration blocks 31/2, 31/3, 31/5 and 31/6). Troll West contains seismic survey ‘NH0301’, which has a coverage of approximately 800 km2, line spacing of 18.75 m in inline (NE–SW) and
12.5 m in crossline (NW–SE) directions, and which images to a
depth of about 3000 ms (millisecond) two-way time (ms TWT).
Troll East contains seismic survey ‘SG9202’, which has a coverage of around 900 km2, line spacing of 25 m in both inline
(east–west) and crossline (north–south) directions, and which
images to a depth of approximately 2400 ms TWT. The surveys
overlap in the centre of the Troll Field. Based on seismic velocity and frequency data, the seismic resolution in the interval of
interest is estimated to be about 15–25 m. Attribute data were
used to understand the gross stratigraphical architecture of the
intervals of interest. However, detailed analysis is complicated
by the occurrence of closely spaced gas–oil and oil–water contacts that combine to produce a prominent ‘flat spot’, which
obscures and distorts seismically resolved stratal architectures.
Detailed seismic analysis is beyond the scope of this paper, and
is the subject of ongoing work.
FACIES ANALYSIS AND WIRELINE-LOG
CALIBRATION
Eleven different facies (A–J) are identified in the Krossfjord and
Fensfjord formations (Table 2, Fig. 4). These facies are grouped
into six facies associations, which are described and interpreted
below. Representative sedimentary logs of each facies association are displayed in Figures 5–7, and cross-plots, which illustrate the quantitative wireline-log character of the facies
associations, are shown in Figure 8.
Facies Association 1: Offshore
Facies Association 1 (FA1) is predominantly composed of
Facies A1 and A2, with minor proportions of Facies I (Table 2),
and is cored primarily within the Heather ‘B’ unit (Fig. 5b).
Whereas Facies A2 is identified in all cored wells across the
study area, Facies A1 is absent in wells located in the eastern
part of the Troll Field.
Description. Facies A1 is a very-fine-grained siltstone with
Belemnites and Terebellina burrows. Facies A2 is a finegrained siltstone with Planolites, Terebellina and Chondrites
burrows (Fig. 5b). Bioturbation intensity is high (5–6 on the
qualitative scale of MacEachern & Bann 2008). Facies A1 and
A2 are distinguished from one another using the prevailing
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241
Krossfjord and Fensfjord formations, Troll Field
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ŽƌĞĚ tĞůů
Fig. 3. Simplified map of the Troll Field
(Fig. 1a) illustrating the distribution of
wells available to this study, major faults
and well correlation panels (modified after
Færseth 1996; Ravnås & Bondevik 1997;
Fraser et al. 2002; NPD 2011).
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EŽƌŵĂů &ĂƵůƚ
^ĞŝƐŵŝĐ ƵďĞ
Table 1. Inventory of core data from the lower Viking Group in the Troll Field. Unit thickness is shown in metres and the percentage of core recovered
is shown in brackets
Field
Well No.
Troll West
31/2-1
31/2-3
31/2-4R
31/3-1
31/5-5
31/6-1
31/6-3
31/6-5
31/6-6
Troll East
Heather ‘B’ unit (m)
63
53
60
19
65
30
20
25
13
(100%)
(100%)
(100%)
(100%)
(100%)
(100%)
(100%)
(100%)
(100%)
Fensfjord Fm (m)
147 (46%)
116 (73%)
105 (100%)
152 (62%)
130 (24%)
202 (43%)
87 (32%)
235 (8%)
228 (23%)
ichnotaxa and grain size. Contacts between the two facies are
gradational over 5– 10 m and FA1 can occur in units that are
up to 60 m thick. Very-coarse- to medium-grained sandstone
beds occur locally in FA1 (Facies I). Beds of Facies I have
sharp bases and gradational tops, and vary in thickness from a
few centimetres to 1 m (e.g. at 1484 m in Fig. 5b). Palynofacies analysis indicates an aerobic environment with relatively
Krossfjord Fm (m)
138 (0%)
78 (0%)
85 (45%)
111 (0%)
>75 (<72%)
56 (0%)
176 (0%)
35 (0%)
29 (0%)
Length of core logged (m)
102.7
116.44
202.8
109.96
114.86
107.5
28.1
42.65
28.15
high salinity, high marine species diversity and low energy
(GeoStrat 2011).
Wireline-log signature. Facies Association 1 is typified by high
gamma-ray values, reflecting its high clay content (Figs 5b and 8a).
Facies A2 has lower gamma-ray values than Facies A1 due to its
slightly coarser grain size. Calcite cemented horizons are easily
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
242
N. E. Holgate et al.
Table 2. Summary of facies (A–J) in the Krossfjord and Fensfjord formations. Core photographs for facies A, C, D, F, G, H, I and J are presented in
Figure 4
Facies
Description
A1
Very-fine-grained, dark grey–very dark green–grey
siltstone. Moderately well sorted with subrounded
to subangular grains. Packages of increased siltstone
content are identified in discrete coarsening-upwards
or fining-upwards sections (<0.5 m). Mica and
carbonaceous fragments common throughout. Pyrite
and glauconite are rare. Bedding is absent
Fine-grained, dark grey–medium grey/brown siltstone
with rare fine-grained sandstone. Moderately well
sorted with subrounded to subangular grains.
Occasional coal fragments (1–2 mm) and glauconite.
Nodular calcite cement is rare and siderite nodules
are occasionally present. Bedding is largely absent
due to bioturbation, apart from rare parallel
laminations
Very-fine- to medium-grained, medium–dark grey/
brown sandstone. Siltstone content is highly
variable. Moderately well sorted with subrounded to
subangular grains. Mica and carbonaceous fragments
are common. Siderite is occasional and pyrite is rare.
Nodular calcite cement (<50 cm thick), wood and
carbonaceous material are rare. Bedding is largely
absent due to bioturbation, with very rare cm-scale
low-angle cross-laminations
Coarsening-upwards very-fine- to coarse-grained,
heterolithic, dark–medium grey sandstone.
Moderately sorted with subrounded to subangular
grains. Calcite cement is occasionally present in
thin beds (<50 cm). Parallel-laminated lamina sets
bounded by low-angle truncation surfaces are
identified as hummocky cross-stratification. Abundant
mica and carbonaceous fragments identified along
laminae. Laminated bed sets are 0.1–0.5 m thick
with sharp, planar to hummocky tops. Bed sets
are interbedded with bioturbated, shaly sandstone.
Occasional shell fragments are organized in a chaotic
manner but are rarely fully disarticulated, in thin
beds (<10 cm)
Medium- to coarse-grained, medium–light grey,
planar laminated to trough and tabular crosslaminated sandstone. Quartz grains are typically clear
to milky, occasionally pinkish. Well sorted but may
occasionally be poorly sorted in thin beds (<15 cm)
with subangular to subrounded grains. Rare mica and
carbonaceous fragments. Rare calcite nodules. Shell
fragments are common throughout. Occasionally,
entire shells are preserved, usually in convex-up
position
Medium- to coarse-grained, medium–light grey
sandstone. Moderately well sorted. Quartz grains are
translucent but occasionally smoky. Carbonaceous
fragments and pyrite are rare. Thin (<5 cm) calcite
nodules are occasionally present. Unit is structureless
with very rare low-angle planar lamination. Broken
shell material is common throughout
Fine- to medium-grained, medium grey sandstone.
Well sorted with subrounded grains. Mica and
siltstone appear draped along laminae highlighting
planar to trough –cross-stratified sandstone beds.
Paired drapes are evident. Dip directions are
commonly bidirectional. Thin shelled bivalves are
present
Sharp-based, fining-upwards, fine- to coarse-grained,
medium grey, moderately- to poorly-sorted sandstone.
Base may contain very coarse-grained sandstone with
rounded grains. Abundant mica and carbonaceous
fragments, along with intense bioturbation towards the
top. Very rare high-angle cross-lamination to parallel
lamination in thin beds (<0.1 m thick) particularly
near the top. Only associated with Facies F
A2
B
C
D
E
F
G
Thickness in
core (m)
Bioturbation and
ichnotaxa
Wireline-log
character
1–10
BI=5–6
(Skolithos,
Terebellina)
GR=58–80 API
DT=60–140 µs/
ft NPHI=0.30–
0.56 p.u.
RHOB=2.2–
2.6 g cm−3
Deposition from suspension in
an oxygenated environment
2–15
BI=5–6
(Terebellina,
Planolites,
Chondrites)
GR=48–76 API
DT=85–150 µs/
ft NPHI=0.11–
0.39 p.u.
RHOB=2.1–
2.4 g cm−3
Deposition from suspension in
a well-oxygenated environment
with very rare sedimentation
from storm processes
1–15
BI=5
(Ophiomorpha,
Skolithos,
Chondrites,
Planolites)
GR=65–70 API
DT=75–160 µs/
ft NPHI=0.35–
0.56 p.u.
RHOB=2.2–
2.7 g cm−3
Settling from hypopycnal plume
or fair-weather suspension
deposition (bioturbated deposits)
alternating with rare combined
flow storm currents (laminated
deposits)
1–5
BI=2–4
(Ophiomorpha,
Skolithos,
Chondrites,
Planolites)
GR=40–100 API
DT=50–120 µs/
ft NPHI=0.08–
0.42 p.u.
RHOB=2.0–
2.4 g cm−3
Storm-generated combined flow
currents (laminated deposits)
alternating with rare fairweather suspension deposition
(bioturbated deposits)
1–6
BI=0–1
GR=45–150 API
DT=60–150 µs/
ft NPHI=0.14–
0.50 p.u.
RHOB=2.1–
2.8 g cm−3
Deposition under high
hydrodynamic energy alternating
from lower flow regime (dunescale trough and tabular crosslaminated sandstone) to upper
flow regime (planar laminated
sandstone) in a marine setting
2–7
BI=0–1
GR=40–130 API
DT=50–130 µs/
ft NPHI=0.04–
0.35 p.u.
RHOB=1.9–
2.5 g cm−3
Deposition dominated by fairweather wave swash activity
1–3
BI=1–5
(Palaeophycus,
Planolites,
Skolithos)
GR=80–110 API
DT=80–140 µs/
ft NPHI=0.12–
0.30 p.u.
RHOB=2.2–
2.6 g cm−3
Deposition with relatively high
hydrodynamic energy under the
influence of tidal currents
0.5–1
BI=4–5
(Palaeophycus,
Planolites,
Skolithos)
GR=40–100 API
DT=60–130 µs/
ft NPHI=0.25–
0.36 p.u.
RHOB=1.9–
2.4 g cm−3
Waning current deposit in a
tidal setting, as suggested by
association with Facies F
Interpretation
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243
Krossfjord and Fensfjord formations, Troll Field
Table 2. (Continued)
Thickness in
core (m)
Facies
Description
H
Fine-grained, grey sandstone interspersed throughout 2–3
with lenses of siltstone and mudstone. Well-sorted
with subrounded to subangular grains. Mica and
carbonaceous material are common. Internal structures
include ripple cross-lamination, isolated ripple sets
and discontinuous laminae, which are evident in ripple
troughs (mm scale). In siltstone-rich parts, lenticular
and flaser bedding are evident. Wavy bedding is also
present. Planar-laminated fine-grained sandstone beds
occur rarely. Micro-faults are common. Body and trace
fossils are typically absent
Sharp-based, fining-upwards, granular- to fine0.1–4
grained, light grey, well-sorted sandstone. Grains are
subrounded to subangular, and quartz is very common.
Carbonaceous material is occasional with very rare
mica. Generally appears structureless with rare planarparallel laminations defined by higher siltstone content.
Body fossils are absent. Bioturbation is variable with
fine-grained sandstone being slightly bioturbated
and coarse-grained sandstones being apparently
structureless
Dark green to grey, poorly sorted, matrix-supported, 0.1–1
medium- to coarse-grained sandstone. Beds are sharp
based and occasionally calcite cemented. Blue- to
smoky- to rose-quartz grains. Matrix contains granules
and pebbles, glauconite, carbonaceous material and
high concentrations of bioclastic fragments and intact
shells. Beds are internally chaotic and structureless.
Grain size typically fines upwards at the cm scale.
Occurs at a distinct stratigraphical position marked by
shifts from proximal to distal facies associations
I
J
Bioturbation and
ichnotaxa
Wireline-log
character
BI=0
GR=60–150 API
DT=60–120 µs/
ft NPHI=0.16–
0.48 p.u.
RHOB=2.2–
2.5 g cm−3
Rhythmically fluctuating tidal
current activity in a protected
setting
BI=0–3
GR=30–80 API
DT=60–110 µs/
ft NPHI=0.12–
0.40 p.u.
RHOB=2.1–
2.4 g cm−3
Storm generated ‘event’ bed in
a suspension-dominated setting,
as suggested by association with
Facies A or a thick waning flow
deposit
BI=0
GR=60–70 API
DT=100–140 µs/
ft NPHI=0.32–
0.40 p.u.
RHOB=2.1–
2.3 g cm−3
Transgressive lag deposit as
indicated by the stratigraphical
position at shifts from proximal
to distal facies associations
Interpretation
BI, bioturbation index; GR, gamma ray; DT, sonic travel time; NPHI, neutron porosity; RHOB, bulk density.
identified and are represented by high-value ‘spikes’ in the density log and low-value ‘spikes’ in the neutron porosity log. Beds
of Facies I within siltstone-dominated successions of Facies A2
are marked by pronounced decreases in neutron porosity and
sonic values, increased resistivity values and a slight decrease in
gamma-ray values. The wireline-log signature of Facies I is
clear where thick beds of this facies are developed; in thinner
beds, however, the response is weaker, and only smaller spikes
in the neutron porosity and sonic logs are observed (e.g. at
1484 m in Fig. 5b).
Interpretation. Facies A is characterized by highly bioturbated,
very-fine-grained sediments, suggesting deposition of fine material from suspension fall-out (Howard & Reineck 1981; Collinson & Thompson 1989). The high concentration of siltstone and
the lack of primary bedding structures suggests offshore deposits
were subject to extensive bioturbation below storm wave base
(MacEachern & Bann 2008), probably in a middle–outer shelf
environment. The very dark colour of Facies A1 indicates a high
organic content, which, when combined with the high bioturbation index, implies deposition in an environment ideal for benthic fauna with high nutrient and oxygen levels, and normal
marine salinity. This interpretation is reinforced by palynofacies
analysis. Facies A1 has a higher siltstone content compared to
Facies A2, which may be indicative of a deeper water environment for the former, which is reinforced by the ichnotaxa present (Pemberton et al. 1992). Facies A1 coarsens upwards into
Facies A2, signifying a shallowing of water depth.
The isolated, sharp-based, very-coarse- to medium-grained
sandstone beds (Facies I) are interpreted to be the product of highenergy events that were able to transport coarse-grained material
into a relatively distal environment. A number of mechanisms have
been proposed for the origin of such deposits, including offshore
sediment transport by major storms, floods, rip currents, river-fed
hyperpycnal flows and tsunamis (Kumar & Sanders 1976;
Gruszczyński et al. 1993; Mulder et al. 2003). Similar interpretations have been proposed for comparable beds in the Sognefjord
Formation (Dreyer et al. 2005). Wells that contain thicker event
beds are located in the northern part of Troll West, closer to the
sediment source inferred for the Sognefjord Formation (Dreyer
et al. 2005).
Facies Association 2: wave-dominated lower
shoreface
Facies Association 2 (FA2) is identified throughout the Fensfjord
Formation in the Troll Field (e.g. Fig. 6a) and in the Krossfjord
Formation in Troll West (Fig. 3).
Description. FA2 is composed of 5–15 m-thick, upwards-coarsening successions of Facies B and C. Bioturbated, very-fine- to
medium-grained sandstone that contain rare low-angle laminations (Facies B) at the base of the association pass gradationally
upwards into very-fine- to medium-grained sandstone that contains rhythmically interbedded, hummocky cross-stratified and
bioturbated intervals (Facies C). Sharp-based, poorly sorted,
structureless beds of granular- to fine-grained, light grey sandstone (Facies I), which are 0.2–0.5 m thick, occur within Facies
B and C. The dominant ichnotaxa recognized in FA2 are Skolithos and Ophiomorpha. Planolites and Chondrites are also evident, in addition to rare, fully disarticulated shell fragments.
Bioturbation decreases in intensity from the base to the top of
the association. Palynofacies analyses indicates an aerobic environment with relatively high salinity, low marine species diversity and low energy (GeoStrat 2011).
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
244
N. E. Holgate et al.
A
B
C
D
E
F
G
H
I
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
245
Krossfjord and Fensfjord formations, Troll Field
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is shown in Figure 3.
FA2 typically overlies other coarsening-upwards successions
within the Fensfjord and Krossfjord formations (e.g. at 1618 m
in Fig. 6a). The lower and upper boundaries of FA2 are sharp;
the upper boundary is occasionally overlain by a dark green–
grey, poorly sorted, matrix supported, medium- to coarse-grained
sandstone (Facies J).
Wireline-log signature. The upwards transition from Facies B to
C is represented on wireline logs by an upwards decrease in
gamma-ray and density-log values, and an upwards increase in
neutron porosity and sonic log values (e.g. from 1618 to 1612 m
in Fig. 6a). The abundance of mica in Facies B and C results in
FA2 having overall high gamma-ray values (Serra & Serra 2003)
(e.g. at 1615 m in Fig. 6a; see also Fig. 8b).
Interpretation. FA2 is defined by the alternations between fairweather suspension settling and more energetic hydrodynamic
conditions. Facies B is composed of interbedded sandstone and
siltstone, which is indicative of fluctuating energy levels (Bourgeois 1980; Dott & Bourgeois 1982; Duke 1985). Siltstone is
deposited via fair-weather suspension settling, whilst sandstone is
deposited through waning, storm-generated suspension currents
(Brenchley 1985). The high bioturbation index of siltstones in
Facies B suggests that they record prolonged fair-weather periods
that allowed biogenic reworking of the sediment. These characteristics are typical of the ‘transition zone’, which is above storm
wave base but below fair-weather wave base (Reineck & Singh
1973), and which is referred to here as the ‘distal lower shoreface’ (sensu Van Wagoner et al. 1990). This zone was only disturbed by large, infrequent storm events. The low-angle, inclined
lamina sets and beds identified in Facies C are interpreted as
hummocky cross-stratification (HCS) (e.g. at 1612.5 m in Fig. 6a).
HCS is the result of combined flow that is formed by a unidirectional current generated by a storm, which carries sand out from
the coast under the influence of high-amplitude waves. The
waves then disperse the sand through oscillatory motion, depositing
Fig. 4. Core photographs illustrating selected facies of the Krossfjord and Fensfjord formations: (a) Facies A, a fine-grained siltstone with Terebellina
trace fossils (31/2-4R at 1498 m); (b) Facies C, a fine-grained sandstone with hummocky cross-stratification (31/6-1 at 1529 m) (NPD 2011); (c) Facies
D, a tabular cross-stratified medium- to coarse-grained sandstone (31/5-5 at 1887 m); (d) Facies F, a cross-stratified sandstone with paired mud-draped
laminations (31/6-6 at 1723 m); (e) Facies F, a cross-stratified sandstone with bidirectional mud-draped laminations (31/6-6 at 1770 m) (NPD 2011);
(f) Facies G, a sharp-based, fining-upwards medium-grained sandstone (31/6-5 at 1714 m); (g) Facies H, a fine-grained sandstone with lenticular bedding
and evidence of micro-faulting (31/6-1 at 1604.5 m); (h) Facies I, a well-sorted, graded, coarse-grained to granular sandstone (31/5-5 at 1866 m) (NPD
2011); and (i) Facies J, a very poorly sorted coarse-grained to granular sandstone with a sharp base (31/2-1 at 1658 m). Photographs are located in the
successions illustrated in Figures 5–7, where possible. The black and white scale bar represents 3 cm.
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
246
N. E. Holgate et al.
it as hummocks (Bourgeois 1980; Dott & Bourgeois 1982; Duke
1985). Similar low-angle, inclined lamina sets and beds are interpreted as HCS in the Sognefjord Formation in the Troll Field
(Stewart et al. 1995; Dreyer et al. 2005). The rhythmic interbedding of bioturbated sandstone and hummocky cross-stratified
sandstone reflects the alternation between fair-weather deposition
and storm deposition, in water depths that lie between fairweather wave base and storm-wave base (Walker 1984; Brenchley 1985). The prevalence of HCS in Facies C indicates a more
proximal lower shoreface location (sensu Van Wagoner et al.
1990) compared to Facies B (Dott & Bourgeois 1982). Thin
(<10 cm), structureless beds of Facies I are interpreted to have
been deposited by gravity-driven or storm-related flows (cf.
Dreyer et al. 2005).
Facies Association 3: wave-dominated upper
shoreface and foreshore
Facies Association 3 (FA3) is identified in the Fensfjord
Formation throughout the Troll Field (Fig. 6a), except in the
upper part of the formation in Troll East. It is also present in the
Krossfjord Formation.
Description. FA3 is 2–15 m thick, and is comprised of Facies D
and E. Medium- to coarse-grained, well-sorted, planar laminated to
trough and tabular cross-bedded sandstone (Facies D) is typically
interbedded with and/or coarsens upwards into medium- to coarsegrained, apparently structureless, sandstone (Facies E). Broken
shell material is common within FA3, although articulated shells
are occasionally present, especially in Facies E (e.g. at 1618 m in
Fig. 6a). Overall, FA3 is poorly bioturbated. FA3 always overlies
FA2 in upwards-coarsening successions. Palynofacies analyses
indicate an aerobic environment with relatively high salinity, low
marine species diversity and high energy (GeoStrat 2011).
Well-log signature. Gamma-ray values in FA3 are usually low
owing to the lack of clay and mica (Fig. 8c). Density values are
also lower than for FA2, reflecting greater porosity in FA3 (Fig.
8c). Variability in the log signature of FA3 is principally due to
patchy calcite cementation (e.g. at 1625.5 m in Fig. 6a).
Interpretation. Facies D lacks bioturbation, and contains an
abundance of planar lamination and trough cross-bedding. The
well-sorted character of the sandstone indicates extensive
reworking, probably in a high-energy marine environment above
fair-weather wave base (i.e. the upper shoreface: sensu Van
Wagoner et al. 1990; see also Walker 1984). The facies lacks
evidence of a tidal influence (e.g. reactivation surfaces, bidirectional current ripples: Nio & Yang 1991). Alternation of trough
cross-bedding and planar lamination can be explained by the
migration of longshore bars and troughs (e.g. Nielsen & Johannessen 2001). The bars were dominated by unidirectional currents, which winnowed out finer-grained material. Migration of
the bars and superimposed 3D dunes resulted in the deposition
of trough cross-bedded intervals. The parallel laminations, however, formed due to the passage of weaker currents through the
inter-dune trough areas, which accounts for the overall finer
grain sizes (cf. Gani & Bhattacharya 2007).
Facies E is common in the upper part of upwards-coarsening
successions of FA3. The coarse-grained, very-well-sorted character of the sandstone in Facies E suggests constant wave action,
which winnowed out finer grains (Hart & Plint 1995). The structureless appearance and rare parallel laminations is consistent
with deposition in a foreshore environment characterized by
swash processes, although similar structures have also been documented on the crest of bar forms (Hunter et al. 1979).
The vertical stacking of FA2 and FA3 to form overall
upwards-coarsening successions is interpreted to represent progradation of a wave-dominated shoreface (Fig. 6a).
Facies Association 4: wave-dominated, tideinfluenced upper shoreface
Facies Association 4 (FA4) is identified in the upper part of the
Fensfjord Formation in Troll East only (Fig. 6b).
Description. FA4 comprises fine- to medium-grained, planar- to
trough-cross stratified sandstone (Facies F). Cross-beds in Facies
F appear bidirectional (e.g. Fig. 4e) and siltstone drapes are
identified along cross-bed foresets (e.g. at 1710 m in Fig. 6b).
These sandstones are interbedded with units of sharp-based, fining-upwards, fine- to coarse-grained sandstone, which are
stacked to form upwards-fining units that are 0.5 m thick (Facies
G). Facies G also contains abundant mica and carbonaceous
fragments, and very rare parallel laminations are identified in
thin beds (<0.1 m). The dominant ichnotaxa in FA4 are Palaeophycus, Planolites and Skolithos. Shell fragments occur sporadically throughout this facies association. Palynofacies analyses
indicate an aerobic to dysaerobic environment with relatively
low salinity, low marine species diversity and relatively low
energy (GeoStrat 2011).
Successions of FA4 are 5–10 m thick and typically overlie
lower shoreface deposits of FA2. FA2, in this context, is
intensely bioturbated (e.g. at 1720 m in Fig. 6b). FA4 also
occurs in association with FA5 in Troll East (Fig. 7a).
Well-log signature. The upwards transition from Facies F to
Facies G is represented by a decrease in gamma-ray and neutron
porosity values, and an increase in density values. This is due to
the coarser grain size and lower mica content of Facies G compared to Facies F. The variable grain size in beds of Facies F
and G gives FA4 an overall serrated appearance on wireline logs
(e.g. at 1712 m in Fig. 6b).
Interpretation. The well-sorted character and abundance of
planar- to trough-cross stratified beds in Facies F suggest a
relatively high-energy depositional environment above fairweather wave base (upper shoreface: sensu Van Wagoner et al.
1990). The occurrence of apparently opposed cross-bed orientations implies episodic reversals in flow direction. Sandstone
laminae are also draped with silt, occasionally displaying
rhythmical silt-layer couplets (cf. Visser 1980). The deposition
of silt may have occurred during slack water periods associated with tidal currents (Nio & Yang 1991). This facies is
therefore interpreted as being deposited in an upper shoreface
environment where fair-weather wave-driven processes were
modulated by tidal influence (cf. Vakarelov et al. 2012).
Facies G consists of sharp-based, coarse-grained, finingupwards sandstone beds, occasionally with a basal lag (e.g. at
1714.5 m in Fig. 6b), suggesting deposition by an energetic
process that was able to erode into the underlying deposits.
The units are thin (0.3–1 m) and commonly have bioturbated
tops, implying that Facies G was deposited under waning flow
conditions. Whilst such deposits can be formed by a number
of processes (e.g. storm-generated rip currents or gravity flows
generated by river floods), the position of this facies within
tide-influenced deposits suggests they could be remnants of
tidal channels (cf. Israel et al. 1987).
FA4 overlies lower shoreface deposits of FA2. In this context, Facies B appears highly bioturbated, which could reflect
increased sediment colonization by burrowing organisms, promoted by tidal current action (Dashtgard et al. 2012). However,
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
247
Krossfjord and Fensfjord formations, Troll Field
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;ĂͿ
0
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0
Fig. 6. (a) Sedimentary log through wave-dominated lower shoreface, and upper shoreface and foreshore facies associations from well 31/2-3 and (b)
sedimentary log through wave-dominated, tide-influenced upper shoreface facies association from well 31/6-5, indicating parasequences bounded by
local transgressive surfaces (TS). The well locations are shown in Figure 3.
there is no direct evidence to support a wave-dominated, tideinfluenced lower shoreface succession, despite Facies B and C
occurring beneath wave-dominated, tide-influenced upper shoreface deposits.
The facies association is only identified in association with
FA4; thin (<3 m) successions of FA5 are typically intercalated
with thicker (5–10 m) successions of FA4. Contacts between
these facies association are sharp.
Facies Association 5: tide-dominated, waveinfluenced embayment
Well-log signature. Gamma-ray, density and neutron porosity
values are nearly uniform within FA5 (Figs 7a and 8e). Gammaray and neutron porosity values appear high and density values
appear low compared to other facies associations. The only variability in these logs is due to the localized occurrence of calcite
cement. In these cases, the gamma-ray and neutron porosity
decreases and the density increases.
Facies Association 5 (FA5) is identified in the middle of the
Fensfjord Formation in Troll East (31/6-1; Fig. 7a).
Description. FA5 consists of fine-grained, well-sorted sandstone
that contains lenses of siltstone or mudstone (Facies H). The
facies association contains ripple cross-lamination, isolated ripple
sets and discontinuous laminae, which occur on a mm scale (e.g.
at 1605 m in Fig. 7a). The lenses of mudstone (> 1 cm thick)
appear either laminated or structureless. Wavy-bedded lamina sets
show regular reversals in the direction of ripple forest dip
between beds. Planar-laminated fine-grained sandstone beds
occur rarely in this facies association. Wavy bedding dominates
Facies H but lenticular bedding and flaser bedding also occur.
Interbedded sandstone and siltstone occur at the decimetre (dm)
scale as the facies fines upwards. Syn-sedimentary micro-faults
are also evident. Synaeresis cracks are not identified. Bioturbation and body fossils are absent. Palynological analyses indicate
brackish conditions with relatively low energy (GeoStrat 2011).
Interpretation. The interbedded rippled sandstone and mudstone
layers suggest periodic fluctuations in hydrodynamic conditions,
from high current velocity, capable of moving sand grains to
form ripples, to slack water conditions, which allowed silt, mud
and mica to settle out of suspension (Reineck & Wunderlich
1968). The planar-laminated sandstone beds are interpreted as
event beds deposited from upper flow-regime conditions, most
probably during storms based on the well-sorted, fine-grained
character of the sandstones and the overall facies context. The
upwards- fining trend seen in Facies H suggests that the overall
hydrodynamic energy of the system was decreasing. The low
bioturbation index may result from a narrow colonization window that is related to high rates of sedimentation (e.g. Gani
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
248
N. E. Holgate et al.
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ϲ ϳϬ
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Z,K>ŽŐ E,W/>ŽŐ
;ŐͬĐŵͲϯͿ
;Ɖ͘Ƶ͘Ϳ
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ϲϲ
0
ϵϴ
ŝŽƚƵƌͲ
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;ŐͬĐŵͲϯͿ
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ϴϵ
tĂǀĞͲĚŽŵŝŶĂƚĞĚ͕ ƟĚĞͲŝŶŇƵĞŶĐĞĚ ƵƉƉĞƌ ƐŚŽƌĞĨĂĐĞ ;&ϰͿ
^ĞƌŝĞƐϯ
WĂƌĂƐĞƋƵĞŶĐĞϯĂ
ϴϲ
ŝŽƚƵƌͲ
'Z>ŽŐ
ďĂƟŽŶ
;W/Ϳ
ŝŶĚĞdž
Ϭ
s& & D s
d^
;ďͿ
&E^&:KZ&KZDd/KEͲt>>ϯϭͬϲͲϭ
&ŝŐ͘ϰŐ
0
ϴϮ
Fig. 7. (a) Tide-dominated, wave-influenced embayment facies association sedimentary log from well 31/6-1 and (b) delta-front facies association
sedimentary log from well 31/5-5 with parasequences bounded by local transgressive surfaces (TS) and basic sequences (Series 1, 2 and 3) bounded by
maximum flooding surfaces (J-). The well locations are shown in Figure 3.
et al. 2005) and/or brackish water conditions, and/or fluctuating
salinities.
Periodic alternation of hydrodynamic energy is common to a
number of tidal and estuarine environments such as subtidal
flats, tidal channels and intertidal flats (e.g. Reineck &
Wunderlich 1968). Flaser and wavy bedding have also been recognized in fluvial (Martin 2000) and lacustrine environments
(Ainsworth et al. 2012). Furthermore, the thin, structureless
mudstone lenses could represent fluid-mud deposits, which have
been identified in tidal–fluvial channel successions, mouth-bar
and terminal distributary channel successions, and delta-front
successions (Ichaso & Dalrymple 2009). However, FA5 is only
identified in association with FA4, which is interpreted as a
wave-dominated, tide-influenced shoreface; this argues against a
fluvial or lacustrine environment of deposition. FA5 is therefore
interpreted to document tidally dominated deposition in a sheltered environment, such as an embayment. There is no evidence
of subaerial exposure, implying deposition in a subtidal setting.
The facies association is commonly associated with FA4, which
suggests it represents shallow-water deposition above a wavedominated, tide-influenced upper shoreface.
Facies Association 6: delta front
Facies Association 6 (FA6) is only identified in the Krossfjord
Formation (well 31/5-5; Fig. 7b).
Description. FA6 is identified in one well only and is 30 m
thick. This facies association is characterized by sharp-based,
fining-upwards, well-sorted beds of medium- to coarse-grained
sandstone (Facies I). These beds, which amalgamate to form
units that are 2–4 m thick, are typically structureless, although
rare planar lamination is observed. Rare (< 1 m thick) intervals
of Facies I are calcite cemented. The tops of the fining-upwards
units consist of 0.2–0.3 m-thick intervals of bioturbated, fine- to
medium-grained sandstone (Facies B). Bioturbation is restricted
to the top of the upwards-fining sandstone beds. No palynofacies analyses were conducted on the Krossfjord Formation.
Well-log signature. FA6 is characterized by uniformly high neutron porosity values, and uniformly low density and gamma-ray
values (Figs 7b and 8f). Thin intervals of calcite cement (< 1 m)
cause a decrease in neutron porosity values and an increase in
density values (e.g. at 1862.5 m in Fig. 7b). Gamma-ray values
are locally increased by high concentrations of carbonaceous
debris (e.g. at 1875 m in Fig. 7b).
Interpretation. We interpret that the fining-upwards beds of structureless and parallel-laminated sandstone were deposited from
high-energy, high-concentration submarine gravity flows, which
were characterized by a high rate of deposition (Lowe 1982;
Middleton 1993). The stacked, amalgamated nature of the beds
implies repeated gravity flows (e.g. at 1875 m in Fig. 7b). Three
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
249
Krossfjord and Fensfjord formations, Troll Field
(b) Wave-dominated lower shoreface Facies Associaon (FA2)
0.32
NPHI (p.u.)
0.40
0.48
0.16
0.24
0.32
NPHI (p.u.)
0.40
0.48
40
0.56
160
0
2.8
2.6
RHOB (g cm-3)
2.4
2.2
2.0
1.8
0.24
0.32
NPHI (p.u.)
0.40
0.48
0.56
3.0
2.8
2.6
RHOB (g cm-3)
2.4
2.2
120
140
160
0.24
0.32
NPHI (p.u.)
0
0.08
0.16
0.24
0.32
0.40
0.48
0.56
0
0.08
0.16
0.24
0.32
0.40
0.48
0.56
NPHI (p.u.)
3.0
160
2.8
2.6
RHOB (g cm-3)
2.4
2.2
60
0.16
0.16
2.0
100
DT (μs/)
40
0.08
0.40
0.48
0.56
20
140
80
140
GR (API)
2.4
120
60
120
2.8
2.6
RHOB (g cm-3)
2.2
2.0
1.8
100
DT (μs/)
1.6
80
0.08
(f) Delta-front Facies Associaon (FA6)
3.0
160
140
120
100
GR (API)
80
60
40
20
60
0
1.8
60
40
0.08
20
0
160
100
160
140
80
140
120
160
GR (API)
2.4
120
100
DT (μs/)
120
2.8
2.6
RHOB (g cm-3)
2.2
2.0
1.8
100
DT (μs/)
1.6
80
80
140
3.0
160
140
120
100
GR (API)
80
60
40
20
60
60
(d) Wave-dominated, de-influenced upper shoreface Facies Associaon (FA4)
(e) Tide-dominated, wave-influenced embayment Facies Associaon (FA5)
40
40
0.56
1.6
0.24
1.6
0.16
(c) Wave-dominated upper shoreface Facies Associaon (FA3)
40
3.0
160
140
120
GR (API)
60
40
0.08
2.0
0
1.8
160
40
60
80
100
DT (μs/)
120
140
160
1.6
140
20
120
100
100
DT (μs/)
80
80
80
2.4
2.2
2.0
1.8
60
1.6
40
20
40
100
2.6
RHOB (g cm-3)
100
80
60
GR (API)
120
2.8
140
3.0
160
(a) Offshore Facies Associaon (FA1)
NPHI (p.u.)
KEY
31/2-1
31/2-3
31/2-4R
31/3-1
31/5-5
31/6-1
31/6-3
31/6-5
31/6-6
Fig. 8. Wireline-log cross-plots of gamma-ray (GR) v. sonic (DT) data, and density (RHOB) v. neutron porosity (NHPI) data. The cross-plots illustrate
the quantitative log character of the facies associations identified in the Krossfjord and Fensfjord formations: (a) offshore; (b) wave-dominated lower
shoreface; (c) wave-dominated upper shoreface and foreshore; (d) wave-dominated, tide-influenced upper shoreface; (e) tide-dominated, waveinfluenced embayment; and (f) delta front. The cross-plots are compiled with data from logged core intervals. The cross-plots illustrate the absence of
clear differences in quantitative log character between many facies associations, which limits their identification in uncored wells. The wireline logs
were, therefore, only used to distinguish sandstone-rich facies associations from mudstone-rich facies associations.
mechanisms may plausibly produce the sediment gravity flows
that deposited the thick-bedded, structureless sandstone of FA6.
First, sustained hyperpycnal flows could be generated by the
introduction of dense, sediment-laden water from rivers into the
basin (Mulder et al. 2003; Plink-Björklund & Steel 2004). Second, repeated, retrogressive failure of sand-rich, shallow-marine
mouth bars could generate turbidity currents (Olariu et al. 2010).
Third, ‘sediment breaching’ (i.e. gradual retrogression of steep,
subaqueous, sand-rich slopes) may generate sustained turbidity
currents (Van Den Berg et al. 2002). The high-density character
of the interpreted gravity flows favours a hyperpycnal flow or
sediment-breaching origin. Based on the coarse grain size and the
thickness of amalgamated beds in FA6, in combination with its
close proximity to the sediment source at the palaeoshoreline, we
interpret that FA6 was deposited in a proximal delta-front environment (cf. Mutti et al. 2000; Olariu et al. 2010).
SEQUENCE STRATIGRAPHICAL FRAMEWORK
A sequence stratigraphical framework has been created for the
Krossfjord and Fensfjord formations in the Troll Field, using the
procedure outlined below. In each cored interval, facies associations are stacked vertically into upwards-shallowing successions
bounded by transgressive surfaces, which are marked by landward
facies shifts (e.g. FA3 overlain by FA2) (Figs 6 and 7). These
upwards-shallowing successions are equivalent to parasequences
(sensu Van Wagoner et al. 1990). Core observations indicate that
parasequences typically have a wave-dominated (FA2 and FA3),
mixed wave- and tide-influenced (FA2, FA4 and FA5) or a fluvial-dominated character (FA6). However, the various sandstoneprone facies associations have a similar wireline-log character
(Fig. 8). As a result, parasequences can be recognized in uncored
intervals and wells by vertical trends in wireline logs (e.g. intervals of upwards-decreasing gamma-ray values bounded by sharp
increases in gamma-ray values) but their internal facies character
cannot be confidently interpreted in the absence of core.
Correlation of groups of parasequences between wells has
been constrained by field-wide mapping of major seismic reflectors and by biostratigraphical data (Figs 9 and 10). A high-resolution biostratigraphical scheme for the Fensfjord Formation in
the Troll Field has identified 13 bioevents and six palynofacies
associations (GeoStrat 2011). Major flooding surfaces, marked
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250
N. E. Holgate et al.
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J46 as a flattened datum surface, (b) corresponding, uninterpreted composite seismic section and (c) geoseismic interpretation along the well-log
correlation panel.
by pronounced landwards facies shifts in vertical successions,
have been calibrated using biostratigraphical data to identify the
maximum flooding surfaces interpreted throughout the northern
North Sea in the widely used stratigraphical scheme of
Partington et al. (1993) (so-called ‘J surfaces’). In addition, and
where data permit, minor transgressive surfaces recognized in
core and wireline-log data have been correlated using the Troll
Field biostratigraphical scheme described above. These have not
been extended or correlated to other studies beyond the Troll
Field. Biostratigraphical control is absent in uncored intervals,
which broadly correspond to the lower Fensfjord Formation and
Krossfjord Formation.
Sequence boundaries (sensu Van Wagoner et al. 1990) have
not been interpreted because no surfaces marked by fluvial incision or subaerial exposure have been identified in core and wireline-log data. Furthermore, palynological analysis has not
conclusively identified a non-marine or marginal-marine assemblage that defines a regionally developed surface (i.e. sequence
boundary) that can be correlated across the Troll Field (GeoStrat
2011). As a consequence, the groups of parasequences (i.e. parasequence sets: sensu Van Wagoner et al. 1990) that are correlated between regional maximum flooding surfaces (‘J surfaces’)
correspond to ‘genetic sequences’ (sensu Galloway 1989). Each
of the parasequence groups that are bound by regional maximum
flooding surfaces is designated as a numbered ‘series’ (or ‘basic
sequence’), following the established convention used to
describe stratigraphical architecture in the Sognefjord Formation
reservoir of the Troll Field (e.g. Dreyer et al. 2005). ‘Series 1’
is bounded by the J32 and J42 maximum flooding surfaces at its
base and top, respectively, and consists of the Heather ‘A’ unit,
the Krossfjord Formation and the lowermost Fensfjord Formation
(Figs 9a and 10a). Series 1 contains eight parasequences, which
are stacked to form a single progradational parasequence set.
‘Series 2’ is bounded by the J42 and J44 maximum flooding
surfaces at its base and top, respectively, and consists of the
lower–middle Fensfjord Formation (Figs 9a and 10a). Series 2
contains three parasequences, the lowest of which constitutes a
progradational parasequence set. The upper two parasequences
are stacked within a retrogradational parasequence set, although
not all parasequences can be distinguished in each well. ‘Series
3’ is bounded by the J44 and J46 maximum flooding surfaces at
its base and top, respectively, and consists of the upper Fensfjord
Formation and the lower Heather ‘B’ unit (Figs 9a and 10a).
Series 3 contains a maximum of 10 parasequences. The lower
five parasequences are stacked to form a progradational parasequence set, although not all five parasequences can be distinguished in each well, and the upper five parasequences constitute
a retrogradational parasequence set. The vertical stacking of parasequences defines an overall progradational architecture in
‘Series 1’, and a progradational–retrogradational architecture in
‘Series 2’ and ‘Series 3’ (Figs 9a, 10a and 11).
Although major and minor flooding surfaces have been identified, systems-tract terminology has not been employed since no
sequence boundaries have been confidently identified, as discussed
above. The lack of evidence for a sequence boundary detailed
above may reflect type-2 sequences where rapid subsidence
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
251
Krossfjord and Fensfjord formations, Troll Field
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Fig. 10. (a) NE–SW-orientated (depositional dip-orientated) well-log correlation panel across Troll West Field (see Fig. 3 for the location), using the
MFS J46 as a flattened datum surface, (b) corresponding, uninterpreted composite seismic section and (c) geoseismic interpretation along the well-log
correlation panel.
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
252
(a)
N. E. Holgate et al.
NW
35.00
GR
4,400 m
31/2-4R
1.90
140.00
RHOB
2.50
35.00
10,500 m
GR
31/2-3
1.90
140.00
RHOB
2.50
7,500 m
35.00
GR
31/3-1
1.90
140.00
RHOB
2.50
35.00
GR
31/6-1
1.90
140.00
RHOB
2.50
35.00
SE
16,700 m
GR
31/6-5
140.00
1.90
RHOB
2.50
35.00
GR
31/6-3
1.90
140.00
RHOB
2.50
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Sogneord Fm
*
**
*
**
**
**
*
***
*
**
**
*
**
**
*
**
**
6b
MFS J42
MFS J46
7a
MFS J44
Fensord Fm
*
**
**
*
**
**
*
6a
5b
Heather “B” unit
MFS J46
**
**
**
**
**
***
**
**
**
Heather “B” unit
50 m
Fensord Fm
Krossord Fm
NE
8,000 m
31/2-3
Sogneord Fm
35.00
GR
140.00
6a
MFS J44
RHOB
2.50
35.00
GR
140.00
1.90
RHOB
31/5-5
2.50
35.00
GR
140.00
1.90
RHOB
2.50
Sogneord Fm
Heather “B” unit
MFS J46
Fensord Fm
1.90
SW
9,200 m
31/2-1
MFS J46
**
*
**
*
*
**
**
**
*
**
**
*
**
***
Heather “B” unit
50 m
Fensord Fm
**
***
7b
Krossord Fm
MFS J42
Krossord Fm
KEY
Offshore (FA1)
Wave-dominated lower shoreface (FA2)
Wave-dominated upper shoreface (FA3)
Wave-dominated, “de-influenced shoreface (FA4)
Tide-dominated, wave-influenced embayment (FA5)
Delta-front (FA6)
Locally Recognised Trangressive Surface
Regional Maximum Flooding Surface
* Biostra“graphic Data Point
Logged Core Interval
Figure Number of Sedimentary Log
7a
(b)
Fig. 11. (a) NW–SE-orientated (depositional strike-orientated) and (b) NE–SW-orientated (depositional dip-orientated) core-log correlation panels across
Troll Field (see Fig. 3 for the location), using MFS J46 as a flattened datum surface.
exceeds the rate of sea-level fall preventing sub-aerial exposure
(Posamentier & Vail 1988). Previous studies focusing on sequence
stratigraphy in extensional rift basins have therefore placed the
sequence boundary between the highstand and transgressive systems tracts (e.g. Posamentier & Allen 1993a, b; Howell & Flint
1996). However, without a detailed understanding of local variations in sediment supply and timing of activity on different fault
segments, it is inappropriate to use systems-tract terminology for
stratigraphical sequences deposited during rifting (e.g. Gawthorpe
et al. 1994). Furthermore, we are unable to explicitly relate the
observed stratal stacking patterns to discrete portions of the eustatic sea-level curve; in the context of the rift setting studied here,
it is likely that stacking patterns are driven by tectonics (i.e. relative sea-level changes) rather than eustacy.
Well correlation panels
The sequence stratigraphical framework and corresponding
facies association distributions are illustrated in three well correlation panels (Figs 9–11). Figures 9 and 10 illustrate wirelinelog-based well correlations of the entire lower Viking Group
(i.e. Heather ‘A’ unit, Krossfjord Formation, Fensfjord
Formation and Heather ‘B’ unit). Figure 11 illustrates core-logbased well correlations of the upper part of the Fensfjord
Formation only. The following subsections describe the sequence
stratigraphical features of each stratigraphical unit.
Heather ‘A’ unit and the Krossfjord Formation. The Heather ‘A’
unit and the Krossfjord Formation are latest Bajocian in age
(165 Ma) and lie above a regionally extensive transgressive surface that caps the Brent Group (MFS J32) (Partington et al.
1993). The top of the Krossfjord Formation does not correspond
to a regional maximum flooding surface but is a minor transgressive surface (Figs 9 and 10). Wells, cores and wireline logs
indicate that the Krossfjord Formation is coarser grained and has
a higher sandstone content than the Fensfjord Formation.
The Krossfjord Formation and the Heather ‘A’ unit have
been subdivided into seven parasequences that are approximately
5–25 m thick. None of the transgressive surfaces that bound
these parasequences have been correlated to regional maximum
flooding surfaces (cf. Partington et al. 1993) owing to a lack of
robust biostratigraphical age constraints.
Well correlations show thickening of offshore mudstone
(Heather ‘A’ unit) towards the north, (Figs 9a and 10a). This
trend corresponds to thinning of the overlying Krossfjord
Formation towards the north of the study area. Seismic data
show no thickening of the Krossfjord–Heather ‘A’ interval
towards or across faults (Figs 9b, c and 10b, c).
Overall, the Krossfjord Formation contains relatively thin
parasequences (c. 5 m thick) at its base, thicker parasequences
(c. 25 m thick) towards its middle of the formation and thinner
parasequences (c. 10 m thick) towards its top (Figs 9a and 10a).
Two distinct facies associations are identified in core in the
upper part of the Krossfjord Formation; well 31/5-5 contains
coarse-grained, delta-front deposits (FA6; Fig. 11b), whereas the
most northerly well studied, 31/2-4R, contains three wave-dominated shoreface parasequences (each c. 15 m thick) bounded by
local transgressive surfaces (FA2 and FA3; Fig. 11a).
Fensfjord Formation. The base of the Fensfjord Formation is
defined by a minor transgressive surface that is locally associated with an approximately 1 m-thick transgressive lag, which is
rich in bioclastic material and is calcite cemented (wells 31/2-4R
and 31/5-5 in Fig. 11). West of the Troll Field, towards the basin
centre, a tongue of Heather Formation mudstones associated
with this transgressive surface separates the Krossfjord and
Fensfjord formations (Husmo et al. 2002). The top of the Fensfjord Formation does not correspond to a regional maximum
flooding surface, and biostratigraphical data suggest that this
lithostratigraphical boundary is diachronous (Fig. 9a).
Biostratigraphical data indicate that two regionally significant
maximum flooding surfaces, the J42 (Early Callovian, 155.5 Ma)
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Three palaeogeographical maps have been reconstructed from
core and wireline-log data (Fig. 12). The maps illustrate the
limit of facies belts at maximum regression within the ‘series’
that are bounded by regional maximum flooding surfaces (Figs
9a, 10a and 11). Because there are fewer well penetrations and
fewer cored wells, the palaeogeographical reconstructions for the
older stratigraphical intervals are less well constrained. Well
data indicate no large-scale thickening across faults during the
deposition of the Krossfjord and Fensfjord formations (Figs 9b,
c and 10b, c), and as a result no active structures are indicated
in the reconstructions. Because no fluvial deposits have been
identified in core, no fluvial point source(s) of sediment input
are shown in the reconstructions. Likewise, evidence for subaerial exposure (e.g. roots, pedogenic alteration) is also lacking in
core, and therefore a subaerially exposed coastal plain is not
shown in the reconstructions (Fig. 12).
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identified within the Fensfjord Formation but occurs in the overlying Heather ‘B’ unit or lowermost part of the Sognefjord
Formation (S. Patruno pers. comm. 2011). The Fensfjord
Formation can be further subdivided into 13 parasequences, each
10–40 m thick, which are correlated across the Troll Field. The
parasequences are of relatively uniform thickness laterally, and
well and seismic data indicate that the Fensfjord Formation itself
is isopachous (Figs 9 and 10). In Troll West, the parasequences
typically comprise wave-dominated shoreface deposits (FA2 and
FA3) (wells 31/2-4R, 31/2-1 and 31/5-5 in Fig. 11). Above maximum flooding surface J44, in an interval that contains abundant
core control, wave-dominated shoreface parasequences commonly pass laterally, towards the east, into mixed, wave- and
tide-influenced parasequences (FA2, FA4 and FA5) (wells 31/23, 31/3-1, 31/6-1, 31/6-5 and 31/6-3 in Fig. 11); the significance
of this observation is discussed below.
Palaeogeographical reconstructions
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2/
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Offshore (FA1)
Wave-dominated shoreface (FA2-3)
Wave-dominated, de-influenced shoreface (FA4)
Tide-dominated, wave-influenced embayment (FA5)
Delta-front (FA6)
Cored Well
Un-cored Well
Well Correlaon
20 km
Fig. 12. Facies-association belt extents at maximum regression in the
Troll Field as suggested by the well correlation panels (Figs 9a, 10a
and 11) during (a) Middle–Late Callovian times (between MFS J44 and
MFS J46), (b) Middle Callovian (between MFS J42 and MFS J44) and
(c) Late Bathonian–Early Callovian (below MFS J42).
and J44 (Middle Callovian, 154 Ma) surfaces, are developed
within the Fensfjord Formation; these surfaces can be correlated
across the Troll Field (Figs 9a and 10a). Regional maximum
flooding surface J46 (Late Callovian, 152 Ma) has not been
Series 1: maximum regression Late Bathonian–Early Callovian,
below MFS J42. A palaeogeographical reconstruction for maximum regression of the Krossfjord Formation, below the regional
maximum flooding surface J42, has been compiled using core
data from five wells and wireline-log data from 19 wells (Fig. 12c).
Deposits of three environments have been recognized for this
time period. Wave-dominated shoreface deposits (FA2 and FA3)
are present in the NW part of Troll West (well 31/2-4R in Fig.
12c), and fluvial-dominated delta-front deposits (FA5) occur in
the western part of Troll West (well 31/5-5 in Fig. 12c). Facies
associations occur as linear belts orientated NNE–SSW across
the study area, as constrained by the occurrence of offshore
deposits (FA1) in uncored wells west of the Troll Field (Figs 9a
and 10a).
Series 2: maximum regression Middle Callovian, below MFS
J44. A palaeogeographical reconstruction for maximum regression of the lower Fensfjord Formation, below the regional maximum flooding surface J44, has been compiled using core data
from five wells and wireline-log data from 18 wells (Fig. 12b).
Wave-dominated shoreface deposits (FA2 and FA3) are identified in three cored wells in Troll West (wells 31/2-3, 31/2-4R
and 31/5-5 in Fig. 12b), and these define a facies-association
belt that extends across the Troll West Field and into the previously offshore area to the NW of the Troll Field. The facies belt
is, therefore, wider than its equivalent in the previous time
period (Fig. 12c; see also Figs 9a and 10a). To the east of this
facies-association belt, tide-dominated, wave-influenced embayment deposits (FA5) are recognized in two cored wells in the
centre of the Troll Field (wells 31/2-3 and 31/6-1 in Fig. 12b).
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254
N. E. Holgate et al.
The lateral extent of this facies-association belt further to the
east is not interpreted owing to the absence of core data. Faciesassociation belts are, again, orientated north–south.
(a)
Lo
ng
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or
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Series 3: maximum regression Middle–Late Callovian, below
MFS J46. A palaeogeographical reconstruction for maximum
regression of the uppermost Fensfjord Formation, above the
regional maximum flooding surface J44, has been compiled using
core data from nine wells and wireline-log data from 18 wells
(Fig. 12a). Wave-dominated shoreface deposits (FA2 and FA3)
are restricted to the western half of Troll West (wells 31/2-1,
31/2-4R and 31/5-5 in Fig. 12a). Tide-dominated, wave-influenced embayment deposits (FA5) extend east across the centre of
the Troll Field (wells 31/2-3 and 31/3-1 in Fig. 12a). Wave-dominated, tide-influenced shoreface deposits (FA4) occupy the
entirety of Troll East (wells 31/6-1, 31/6-3, 31/6-5 and 31/6-6 in
Fig. 12a). Offshore deposits (FA1) are identified to the west of
the Troll Field in uncored wells (Figs 9a and 10a). Facies-association belts are, again, orientated broadly north–south but there
are lateral variations in both thickness and facies distribution
(e.g. the tide-dominated, wave-influenced embayment facies-association belt thins and pinches out towards the south) (Fig. 12a).
The palaeogeographical reconstructions highlight temporal
and spatial variations in a depositional process regime (e.g. the
dominance of wave, tide and fluvial processes) during deposition of the Krossfjord and Fensfjord formations. The western
part of each reconstruction consistently shows that wave-dominated shoreface deposits (FA2 and FA3) form the outer part of
the sandstone tongues that pinch-out towards the west and pass
basinwards into offshore deposits. The eastern part of each
reconstruction indicates a more variable process regime, with
significant tidal and fluvial influence. The importance of a tidal
influence appears to increase through time, becoming progressively more prominent from the Krossfjord Formation to the
upper Fensfjord Formation (Figs 11 and 12), although it should
be noted that core data from Troll East is only available to constrain the youngest reconstruction (Fig. 12a). In addition, the
following features occur throughout deposition of the Krossfjord
and Fensfjord formations: (1) no subaerially exposed coastal
plain deposits are identified in the study area; (2) facies-association belts are orientated NNE–SSW; and (3) facies-association
belts are of similar width across the study area. These various
features are addressed by depositional models presented below.
Se
s1
rie
Se
km
2
KEY
Offshore (FA1)
Wave-dominated lower shoreface (FA2)
Wave-dominated upper shoreface (FA3)
Wave-dominated, de-influenced shoreface (FA4)
Tide-dominated, wave-influenced embayment (FA5)
Maximum Flooding Surface (J-Surface)
Studied Cored Well
DISCUSSION: DEPOSITIONAL MODEL
FOR THE KROSSFJORD AND FENSFJORD
FORMATIONS
The well correlations and palaeogeographical reconstructions presented above (Figs 11 and 12) highlight the complex spatial and
temporal distributions of facies-association belts within the
Krossfjord and Fensfjord formations of the Troll Field, albeit
Fig. 13. Block diagrams of depositional models illustrating the lateral
change from mixed wave- and tide-influenced deposits to wavedominated shoreface deposits from east to west across the Troll
Field. Two end-member models are proposed: (a) spatial variation in
depositional environments with a wave-driven spit system fronting a
tide-influenced back basin; and (b) temporal variation in depositional
environments with an early tide-dominated, wave-influenced embayment
and shoreface developed on the inner–middle shelf (t = 1), evolving
into a wave-dominated shoreface as it progrades to the outer shelf
(t = 2). Coastal plain deposits are absent in the core, implying that they
were either not deposited due to development of a broad subaqueous
delta platform or they were removed by later transgressive erosion; the
latter is implied in the block diagrams.
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Krossfjord and Fensfjord formations, Troll Field
255
within a broadly similar range of shallow-marine environments.
The facies associations and stratigraphical components recognized in the Krossfjord and Fensfjord formations are similar to
those of the overlying Sognefjord Formation (Dreyer et al. 2005),
suggesting that the same depositional model(s) may potentially
be applicable to all three sandstone-prone formations in the
Viking Group. In the following subsections the following three
key aspects of the sedimentology and stratigraphical architecture
of the Krossfjord and Fensfjord formations are discussed: (1) the
east to west variation in depositional environments across the
Troll Field; (2) the vertical increase in abundance of tide-influenced deposits; and (3) the absence of coastal plain deposits.
and contain abundant topographical restrictions, which may
locally amplify tidal range (Plink-Björklund 2012). With continued progradation, the width of the shelfal platform is decreased
and wave processes become increasingly dominant, as illustrated
for late progradation (Fig. 13b). The gradual change in the depositional process regime was driven by progradation of the shallow-marine depositional system, which reflects the interplay
between sediment supply, accommodation and basin physiography (Ainsworth et al. 2008). Similar depositional models have
been proposed for the Holocene Mekong River Delta (Ta et al.
2002) and the Holocene Song Hong (Red River) Delta (Tanabe
et al. 2006).
East to west change from mixed wave- and tideinfluenced deposits to wave-dominated deposits in
the upper Fensfjord Formation
Vertical increase in abundance of tide-influenced
deposits
Series 3, the upper part of the Fensfjord Formation (MFS J44–
MFS J46), is characterized by pronounced partitioning between
wave-dominated shoreface deposits in the west of the Troll Field
and a mixed wave- and tide-influenced environment in the east
of the field (Figs 11a and 12a). The change can be explained by
spatial variation in the depositional process regime (Fig. 13a),
temporal variation in the process regime (Fig. 13b) or a combination of the two (Fig. 13). In each model, the source(s) of fluvial sediment input to the shoreline is inferred to have been
situated to the north of the Troll Field; this is consistent with
previous interpretations (Fraser et al. 2002; Husmo et al. 2002;
Dreyer et al. 2005) and is supported by the absence of fluvial
deposits in core. The shoreline position is interpreted to have
been consistently north–south orientated, in agreement with the
linear arrangement of facies-association belts (Fig. 12).
The first depositional model (Fig. 13a) illustrates spatial variation in coeval environments. Sediment was supplied from a fluvio-deltaic source in the north, and redistributed through
wave-generated, southward-directed longshore currents to form a
spit in Troll West. The seawards face of the spit consists of a
wave-dominated shoreface. The spit protects landwards areas from
wave energy, which therefore appear to contain relatively stronger,
and perhaps locally amplified, tidal energy in a tide-dominated
embayment and back-basin setting in Troll East. Similar models
have been proposed for the Sognefjord Formation of the Troll
Field (Dreyer et al. 2005) and the Cretaceous Frewens Delta, US
Western Interior (Willis et al. 1999), both in the context of asymmetrical delta systems (Bhattacharya & Giosan 2003). The
Holocene Maguelone shoreline, SE France (Raynal et al. 2009),
which is starved of fluvial sediment input, also displays a similar
shoreline morphology, with sand spits fronting lagoons. However,
the area immediately landwards of the spit barrier is typically
composed of terrestrial vegetation and peat deposits (e.g. Nielsen
& Johannessen 2001), neither of which is identified in cored successions in the Troll Field. Furthermore, foreshore deposits in spit
systems commonly contain roots (e.g. Nielsen & Johannessen
2008), which are also lacking.
The second depositional model (Fig. 13b) illustrates temporal
variation in environments, with early progradation of a tide-dominated, embayed shoreline to later progradation of a mixed waveand tide-influenced shoreface, and finally progradation of a
wave-dominated shoreface. A wave-dominated, tide-influenced
environment is interpreted to exist during early progradation due
to the wide-shelfal platform in front of the shoreline, which
increases tidal resonance and decreases the effect of wave energy
through friction (Hubbard et al. 1979; Pugh 1987; Ainsworth
et al. 2011). Tidal embayments are created through topographical
restrictions such as barrier islands (e.g. Oertel 1985). It has also
been suggested that inner-shelf deltaic shorelines are irregular
Well correlations of cored wells in the Troll Field highlight an
increasing prevalence of tide-influenced deposits vertically
through the Krossfjord and Fensfjord formations (Fig. 11),
although it should be noted that the dataset is biased towards
‘Series 3’ in the upper part of the Fensfjord Formation (MFS
J44–MFS J46). The pattern of upwards-increasing tidal influence
could record the progressive progradation in ‘Series 1’ of parasequences (Fig. 9a) that are constructed via the mechanisms
depicted in either depositional model (Fig. 13). However, the
same architecture cannot be invoked for ‘Series 2’ and ‘Series
3’, which each exhibit progradational–retrogradational stacking
of parasequences (Figs 9a, 10a and 11). More likely, the
upwards increase in tidal influence reflects the change from progradational to retrogradational stacking in ‘Series 2’ and ‘Series
3’ (Figs 9a, 10a and 11), and from progradational to retrogradational stacking of the three ‘series’ (as noted by Steel 1993;
Stewart et al. 1995; Husmo et al. 2002). Numerous studies document the preferential development and preservation of tidally
influenced deposits in net-transgressive strata (e.g. Nio & Yang
1991; Sixsmith et al. 2008; Kieft et al. 2011).
Absence of coastal plain deposits
Coastal plain deposits are absent in cores from the Krossfjord
and Fensfjord formations because either: (1) palaeosols were
originally developed in each parasequence and then removed by
transgressive erosion (i.e. ravinement); (2) palaeosols were not
developed due to forced regression during relative sea-level fall;
or (3) palaeosols were not developed due to construction of a
broad, shallow, subaqueous platform during each parasequencescale progradational episode.
Transgressive surfaces are identified at parasequence boundaries in both formations (Figs 9a, 10a and 11) and many are associated with lags that record erosional winnowing of the substrate
(e.g. Fig. 4i). Transgressive erosion can remove up to 20 m of
the substrate (Demarest & Kraft 1987) with such deep erosion
being generally associated with channelized tidal scour. Forced
regression during falling relative sea level results in the accumulation of thin, attenuated coastal plain deposits that are more
readily removed by transgressive erosion than the thicker coastal
plain intervals accumulated during normal regression (e.g.
Posamentier & Morris 2000). However, the product of such
deep erosion related to channelized tidal scour is a high-relief
erosional surface lined by large angular shale clasts (Cattaneo &
Steel 2003). Such features are not identified in core data and
therefore argue against this explanation for the absence of
coastal plain deposits.
Forced regression during falling sea level can also result in a
complete absence of coastal plain facies. Three of the eight criteria
used to identify forced regressive deposits by Posamentier & Morris
(2000) are recognized in the Krossfjord and Fensfjord formations:
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N. E. Holgate et al.
(1) the absence of fluvial or coastal plain facies capping regressive
successions; (2) increased average grain size in regressive deposits
in a proximal to distal direction due to the cannibalization and
redistribution of older, proximal highstand sediments; and (3) the
long distance of regression and anomalously thin character of parasequences due to decreased accommodation during lowering of
relative sea level. Steel (1993) previously used the first and third of
these criteria to propose forced regression for the development of
parasequences in the Viking Group. However, two criteria identified by Posamentier & Morris (2000) are absent: (1) sharp-based
shoreface deposits indicative of erosion of shelf deposits due to the
lowering of wave base during falling relative sea level; and (2) a
zone of shallow-marine sediment bypass as a result of sea-level fall,
sometimes expressed as the detachment of lowstand shoreface
deposits from their highstand precursor shorefaces. Furthermore,
three criteria identified by Posamentier & Morris (2000) are indeterminable and therefore require further detailed analysis of seismic
data including: (1) the progressive reduction in relief of clinoforms
going from proximal to distal due to progradation into progressively
shallower water; (2) seawards-dipping bounding surfaces on the top
of parasequences due to the lowering of sea level; and (3) the presence of ‘foreshortened’ stratigraphical sections where the decompacted thickness of a coarsening-upwards sequence is less than the
palaeowater depth. Therefore, conclusive evidence of forced regression appears to be absent but this may reflect the sparse distribution
of core and well data in the Troll Field and surrounding area, and
the limited analysis to date of clinoform trajectories in seismic data.
An alternative interpretation is that palaeosols were never
developed during each progradational episode. This interpretation implies that the area of the Troll Field was subaqueous
throughout deposition of the Krossfjord and Fensfjord formations, and that a broad, shallow, subaqueous platform was
repeatedly constructed during each parasequence-scale progradational episode. The drowning of a broad, shallow platform during subsequent transgression may also have promoted the
development of tidal embayments behind retreating barrier
islands and spits. The development of broad subaqueous platforms is common in many modern deltas that are subject to significant wave and tidal action (e.g. Swenson et al. 2005;
Plink-Björklund 2012), such as the Yangtze Delta, East China
Sea (Hori et al. 2002). The development of broad, subaqueous
platforms have also been interpreted in a handful of ancient
examples, including the Cretaceous Wise Gulch, Berry Gulch
and Morapos sandstones, US Western Interior (Hampson et al.
2008). Furthermore, through the detailed examination of clinoforms imaged in seismic data from the Troll Field, the development of a fully subaqueous deltaic system is proposed to explain
the lack of coastal plain facies in the stratigraphically younger
Sognefjord Formation (S. Patruno pers. comm. 2012).
CONCLUSIONS
The Middle–Upper Jurassic Krossfjord and Fensfjord formations
are two shallow-marine sandstone tongues that form important
secondary reservoirs in the super-giant Troll Field, and are prospective in surrounding areas of the Horda Platform on the eastern margin of the Viking Graben, northern North Sea.
Regionally, both formations thin and pinch out into offshore
shales of the Heather Formation towards the west, beyond the
limit of the Horda Platform. This paper presents the first detailed
sedimentological and stratigraphical analysis of the two formations in the Troll Field, as an aid to predicting reservoir distribution and character. The main conclusions of this core- and
wireline-log-based analysis of the Krossfjord and Fensfjord formations in the Troll Field are summarized below.
1. Core observations indicate that mixed-influenced deltaic,
shoreline and shelf environments were in existence during
the Middle Jurassic in the area of the Troll Field. Palaeogeographical reconstructions of maximum regression show
facies-association belts of similar width, orientation and distribution. A wide (10–20 km) belt of north–south-trending,
wave-dominated shoreface deposits is present in the western
part of the Troll Field. The eastern part of the field contains
more irregular (0–20 km wide), north–south-trending belts of
mixed wave- and tide-influenced shoreface, tide-dominated
embayment, and/or fluvial-dominated delta-front deposits. The change from tide-influenced deposits in the east to
wave-dominated deposits in the west can be attributed either
to spatial variation in the depositional process regime within
an asymmetrical delta fronted by a spit, or to temporal variation in the depositional process regime as the system prograded from a sheltered, inner-shelf location in the east to an
exposed, outer-shelf location in the west.
2. Correlation between wells is constrained by field-wide
mapping of major seismic reflectors at base-Heather ‘A’,
top-Krossfjord and top-Fensfjord levels, combined with recognition of biostratigraphically distinctive, regional maximum flooding surfaces (J32, J42, J44 and J46) in cored
wells. This framework allows recognition of three ‘series’
bounded by the regional maximum flooding surfaces.
Analysis of the entire stratigraphical interval, its constituent ‘series’ and their component parasequences indicate
relatively uniform thicknesses across the extent of the Troll
Field, implying the absence of any major structural control
on sedimentation during the Middle Jurassic in this area.
3. Coastal plain deposits are not identified in the Krossfjord
and Fensfjord formations in the Troll Field. The absence
may be attributed to the development of a broad, shallow,
subaqueous platform across the Troll Field during repeated
parasequence-scale regressions, to transgressive erosion at
the top of each parasequence or to forced regression during falling sea level for each parasequence-scale regression.
Forced regression is consistent with the thin, laterally extensive character of parasequences in the Viking Group over the
Horda Platform and areas adjacent areas to the west.
We would like to thank Paul Whipp, Theresa Lloyd-Lodden, Ian Sharp,
Stefano Patruno, Gavin Elliott, Howard Johnson, Peter Allison and
Aruna Mannie for discussions during the course of this study, and Statoil
ASA for providing data. We thank Bruce Ainsworth, John Underhill and
an anonymous reviewer for their insightful and constructive reviews and
editorial comments. Partners in the Troll production licenses PL054,
PL085, PL085 B & PL085 C (Petoro AS, AS Norske Shell, Statoil ASA,
ConocoPhillips Norge & Total E&P Norge AS) are thanked for supporting the provision of data to undertake this study and for their permission
to publish the results. The views expressed in this paper are the authors
and do not necessarily represent those of the Troll license partners.
Thanks also to Schlumberger Limited for provision of the Petrel seismic
and well interpretation software via an academic software donation.
REFERENCES
Ainsworth, R.B., Flint, S.S. & Howell, J.A. 2008. Predicting coastal depositional style: Influence of basin morphology and accommodation to
sediment supply ratio within a sequence stratigraphic framework. In:
Hampson, G.J., Steel, R., Burgess, P.B. & Dalrymple, R.W. (eds) Recent
Advances in Models of Siliciclastic Shallow-Marine Stratigraphy. SEPM,
Special Publications, 90, 237–263.
Ainsworth, R.B., Vakarelov, B.K. & Nanson, R.A. 2011. Dynamic spatial
and temporal prediction of changes in depositional processes on clastic shorelines: Toward improved subsurface uncertainty reduction and
management. American Association of Petroleum Geologists Bulletin,
95, 267–297.
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
Krossfjord and Fensfjord formations, Troll Field
Ainsworth, R.B., Hasiotis, S.T. et al. 2012. Tidal signatures in an intracratonic playa lake. Geology, 40, 607–610.
Bhattacharya, J.P. & Giosan, L. 2003. Wave-influenced deltas:
Geomorphological implications for facies reconstruction. Sedimentology,
50, 187–210.
Bockelie, J.F. & Howard, A. 1984. Systematic Description of Jurassic Trace
Fossils as They Would Appear in Cored Sections. Norsk Hydro Research
Centre, Norway.
Bourgeois, J. 1980. A transgressive shelf sequence exhibiting hummocky
stratification; the Cape Sebastian Sandstone (Upper Cretaceous), southwestern Oregon. Journal of Sedimentary Research, 50, 681–702.
Brenchley, P.J. 1985. Storm influenced sandstone beds. Modern Geology, 9,
369–396.
Cattaneo, A. & Steel, R.J. 2003. Transgressive deposits: A review of their
variability. Earth-Science Reviews, 62, 187–228.
Collinson, J.D. & Thompson, D.B. 1989. Sedimentary Structures. Unwin
Hyman, London.
Dashtgard, S.E., MacEachern, J.A., Frey, S.E. & Gingras, M.K. 2012. Tidal
effects on the shoreface: Towards a conceptual framework. Sedimentary
Geology, 279, 42–61.
Davies, R.J., Turner, J.D. & Underhill, J.R. 2001. Sequential dip-slip fault
movement during rifting: A new model for the evolution of the Jurassic
trilete North Sea rift system. Petroleum Geoscience, 7, 371–388.
Demarest, J.M. & Kraft, J.C. 1987. Stratigraphic record of Quaternary sea
levels: Implications for more ancient strata. In: Nummedal, D., Pilkey,
O.H. & Howard, J.D. (eds) Sea Level Fluctuation and Coastal Evolution.
SEPM, Special Publications, 41, 223–239.
Dott, R.H. & Bourgeois, J. 1982. Hummocky stratification: Significance of its
variable bedding sequences. Geological Society of America Bulletin, 93, 663.
Dreyer, T., Whitaker, M., Dexter, J., Flesche, H. & Larsen, E. 2005. From
spit system to tide-dominated delta: Integrated reservoir model of the
Upper Jurassic Sognefjord Formation on the Troll West Field. In: Doré,
A.G. & Vining, B.A. (eds) Petroleum Geology: North-West Europe
and Global Perspectives – Proceedings of the 6th Petroleum Geology
Conference. Geological Society, London, 6, 423–448.
Duke, W.L. 1985. Hummocky cross-stratification, tropical hurricanes, and
intense winter storms. Sedimentology, 32, 167–194.
Færseth, R.B. 1996. Interaction of Permo-Triassic and Jurassic extensional
fault-blocks during the development of the northern North Sea. Journal of
the Geological Society, 153, 931–944.
Færseth, R.B. & Ravnås, R. 1998. Evolution of the Oseberg fault-block
in context of the northern north sea structural framework. Marine and
Petroleum Geology, 15, 467–490.
Fossen, H., Hesthammer, J., Johansen, T.E.S. & Sygnabere, T.O. 2003.
Structural geology of the Huldra Field, northern North Sea – A major
tilted fault block at the eastern edge of the Horda Platform. Marine and
Petroleum Geology, 20, 1105–1118.
Fraser, S.I., Robinson, A.M., Johnson, H.D., Underhill, J. & Kadolsky, D.
2002. Upper Jurassic. In: Evans, D., Graham, C., Armour, A. & Bathurst,
P. (eds) The Millennium Atlas: Petroleum Geology of the Central and
Northern North Sea. Geological Society, London, 157–189.
Galloway, W.E. 1989. Genetic stratigraphic sequences in basin analysis; I,
Architecture and genesis of flooding-surface bounded depositional units.
American Association of Petroleum Geologists Bulletin, 73, 125–142.
Gani, M.R. & Bhattacharya, J.P. 2007. Basic building blocks and process
variability of a Cretaceous delta: Internal facies architecture reveals a
more dynamic interaction of river, wave, and tidal processes than is indicated by external shape. Journal of Sedimentary Research, 77, 284–302.
Gani, M.R., Bhattacharya, J.P. & MacEachern, J.A. 2005. Using ichnology to
determine relative influence of waves, storms, tides. and rivers in deltaic
deposits. examples from Cretaceous Western Interior Seaway, U.S.A. In:
MacEachern, J.A., Bann, K.L., Gingras, M.K. & Pemberton, S.G. (eds)
Applied Ichnology. SEPM, Short Course Notes, 52, 209–225.
Gawthorpe, R.L., Fraser, A.J. & Collier, R.E.L. 1994. Sequence stratigraphy
in active extensional basins: Implications for the interpretation of ancient
basin-fills. Marine and Petroleum Geology, 11, 642–658.
GeoStrat. 2011. Biostratigraphic and Palynofacies Evaluation of the
Fensfjord Formation From Five Troll Field Wells. GeoStrat, Strathaven,
Lanarkshire.
Gruszczyński, M., Rudowski, S., Semil, J., Słomiński, J. & Zrobek, J. 1993.
Rip currents as a geological tool. Sedimentology, 40, 217–236.
Hampson, G.J., Rodriguez, A.B., Storms, J.E.A., Johnson, H.D. & Meyer,
C.T. 2008. Geomorphology and high-resolution stratigraphy of progradational wave-dominated shoreline deposits: Impact on reservoir-scale facies
architecture. In: Hampson, G.J., Steel, R.J., Burgess, P.B. & Dalrymple,
R.W. (eds) Recent Advances in Models of Siliciclastic Shallow-Marine
Stratigraphy. SEPM, Special Publications, 90, 117–142.
257
Hart, B.S. & Plint, A.G. 1995. Gravelly shoreface and beach deposits. In:
Plint, A.G. (ed.) Sedimentary Facies Analysis: A Tribute to the Research
and Teaching of Harold G. Reading. International Association of
Sedimentologists, Special Publications, 22, 75–90.
Hellem, T., Kjemperud, A. & Øvrebø, O.K. 1986. The Troll field: A geological/geophysical model established by PL085. In: Spencer, A.M. (ed.)
Habitat of Hydrocarbons on the Norwegian Continental Shelf. Graham &
Trotman, London, 217–238.
Hesthammer, J., Jourdan, C.A., Nielsen, P.E., Ekern, T.E. & Gibbons, K.A.
1999. A tectonostratigraphic framework for the Statfjord Field, northern
North Sea. Petroleum Geoscience, 5, 241–256.
Hori, K., Saito, Y., Zhao, Q. & Wang, P. 2002. Architecture and evolution of
the tide-dominated Changjiang (Yangtze) River delta, China. Sedimentary
Geology, 146, 249–264.
Howard, J.D. & Reineck, H.-E. 1981. Depositional facies of high-energy
beach-to-offshore sequence; comparison with low-energy sequence.
American Association of Petroleum Geologists Bulletin, 65, 807–830.
Howell, J.A. & Flint, S.S. 1996. A model for high resolution sequence stratigraphy within extensional basins. In: Howell, J.A. & Aitken, J.F. (eds)
High Resolution Sequence Stratigraphy: Innovations and Applications.
Geological Society, London, Special Publications, 104, 129–137.
Hubbard, D.K., Oertel, G. & Nummedal, D. 1979. The role of waves and
tidal currents in the development of tidal-inlet sedimentary structures and
sand body geometry; examples from North Carolina, South Carolina, and
Georgia. Journal of Sedimentary Research, 49, 1073–1091.
Hunter, R.E., Clifton, H.E. & Phillips, R.L. 1979. Depositional processes,
sedimentary structures, and predicted vertical sequences in barred
nearshore systems, southern Oregon coast. Journal of Sedimentary
Research, 49, 711–726.
Husmo, T., Hamar, G.P., Høiland, O. et al. 2002. Lower and Middle
Jurassic. In: Evans, D., Graham, C., Armour, A. & Bathurst, P. (eds) The
Millennium Atlas: Petroleum Geology of the Central and Northern North
Sea. Geological Society, London, 129–155.
Ichaso, A.A. & Dalrymple, R.W. 2009. Tide- and wave-generated fluid mud
deposits in the Tilje Formation (Jurassic), offshore Norway. Geology, 37,
539–542.
Israel, A.M., Ethridge, F.G. & Estes, E.L. 1987. A sedimentologic description of a microtidal, flood-tidal delta, San Luis Pass, Texas. Journal of
Sedimentary Research, 57, 288–300.
Johannessen, E.P., Mjøs, R., Renshaw, D., Dalland, A. & Jacobsen, T. 1995.
Northern limit of the ‘Brent Delta’ at the Tampen Spur – a sequence
stratigraphic approach for sandstone prediction. In: Steel, R.J., Felt,
V.L., Johannessen, E.P. & Mathieu, C. (eds) Sequence Stratigraphy on
the Northwest European Margin. Norwegian Petroleum Society, Special
Publications, 5, 213–256.
Kieft, R.L., Hampson, G.J., Jackson, C.A.-L. & Larsen, E. 2011. Stratigraphic
architecture of a net-transgressive marginal- to shallow-marine succession: Upper Almond Formation, Rock Springs Uplift, Wyoming, U.S.A.
Journal of Sedimentary Research, 81, 513–533.
Kumar, N. & Sanders, J.E. 1976. Characteristics of shoreface storm deposits;
modern and ancient examples. Journal of Sedimentary Research, 46, 145–162.
Lowe, D.R. 1982. Sediment gravity flows; II, Depositional models with special reference to the deposits of high-density turbidity currents. Journal of
Sedimentary Research, 52, 279–297.
MacEachern, J.A. & Bann, K.L. 2008. The role of Ichnology in refining
shallow marine facies models. In: Hampson, G.J., Steel, R.J., Burgess,
P.B. & Dalrymple, R.W. (eds) Recent Advances in Models of Siliciclastic
Shallow-Marine Stratigraphy. SEPM, Special Publications, 90, 73–116.
Martin, A.J. 2000. Flaser and wavy bedding in ephemeral streams: A modern
and an ancient example. Sedimentary Geology, 136, 1–5.
Middleton, G.V. 1993. Sediment deposition from turbidity currents. Annual
Review of Earth and Planetary Sciences, 21, 89–114.
Mulder, T., Syvitski, J.P.M., Migeon, S., Faugères, J.-C. & Savoye, B. 2003.
Marine hyperpycnal flows: Initiation, behavior and related deposits. A
review. Marine and Petroleum Geology, 20, 861–882.
Mutti, E., Tinterri, R., Di Biase, D., Fava, L., Mavilla, M., Angella, S. &
Calabrese, L. 2000. Delta front facies associations of ancient flood
dominated fluvio-deltaic systems. Revista de la Sociedad Geológica de
España, 13, 165–190.
Nielsen, L.H. & Johannessen, P.N. 2001. Accretionary, forced regressive
shoreface sands of the Holocene-Recent Skagen Odde spit complex.
Denmark – a possible outcrop analogue to fault-attached shoreface sandstone reservoirs. In: Martinsen, O.J. & Dreyer, T. (eds) Sedimentary
Environments Offshore Norway – Palaeozoic to Recent. Norwegian
Petroleum Society, Special Publications, 10, 457–472.
Nielsen, L.H. & Johannessen, P.N. 2008. Are some isolated shelf sandstone
ridges in the Cretaceous Western Interior Seaway transgressed, detached
Downloaded from http://pg.lyellcollection.org/ at Oregon State University on December 1, 2014
258
N. E. Holgate et al.
spit systems? In: Hampson, G.J., Steel, R.J., Burgess, P.B. & Dalrymple,
R.W. (eds) Recent Advances in Models of Siliciclastic Shallow-Marine
Stratigraphy. SEPM, Special Publications, 90, 333–354.
Nio, S.D. & Yang, C.S. 1991. Sea-level fluctuations and the geometric variability of tide-dominated sandbodies. Sedimentary Geology, 70, 161–
172.179-193.
NPD 2011. [online] http://factpages.npd.no/factpages/. [Accessed 10 January
2011.]
Oertel, G.F. 1985. The barrier island system. Marine Geology, 63, 1–18.
Olariu, C., Steel, R.J. & Petter, A.L. 2010. Delta-front hyperpycnal bed
geometry and implications for reservoir modeling: Cretaceous Panther
Tongue delta, Book Cliffs, Utah. American Association of Petroleum
Geologists Bulletin, 94, 819–845.
Osborne, P. & Evans, S. 1987. The Troll Field: Reservoir geology and field
development planning. In: Buller, A.T. & Kleppe, J. (eds) North Sea Oil
and Gas Reservoirs. Graham & Trotman. London, 39–60.
Partington, M.A., Copestake, P., Mitchener, B.C. & Underhill, J.R. 1993.
Biostratigraphic calibration of genetic stratigraphic sequences in the
Jurassic–lowermost Cretaceous (Hettangian to Ryazanian) of the North
Sea and adjacent areas. In: Parker, J.R. (ed.) Petroleum Geology of
Northwest Europe: Proceedings of the 4th Conference. Geological
Society, London, 4, 371–386.
Pemberton, S.G. MacEachern, J.A. & Frey, R.W. 1992. Trace fossil facies models: their environmental and allostratigraphic significance. In: Walker, R.G.
& James, N.P. (eds) Facies Models: A Response to Sea-Level Changes.
Geological Association of Canada, Newfoundland, 47–72.
Plink-Björklund, P. 2012. Effects of tides on deltaic deposition: Causes and
responses. Sedimentary Geology, 279, 107–133.
Plink-Björklund, P. & Steel, R.J. 2004. Initiation of turbidity currents:
Outcrop evidence for Eocene hyperpycnal flow turbidites. Sedimentary
Geology, 165, 29–52.
Posamentier, H.W. & Allen, G.P. 1993a. Siliciclastic sequence stratigraphic
patterns in foreland, ramp-type basins. Geology, 21, 455–458.
Posamentier, H.W. & Allen, G.P. 1993b. Variability of the sequence stratigraphic model: Effects of local basin factors. Sedimentary Geology, 86,
91–109.
Posamentier, H.W. & Morris, W.R. 2000. Aspects of the stratal architecture of forced regressive deposits. In: Hunt, D. & Gawthorpe, R.L.
(eds) Sedimentary Responses to Forced Regressions. Geological Society,
London, Special Publications, 172, 19–46.
Posamentier, H. & Vail, P.R. 1988. Eustatic controls on clastic deposition
II – sequence and systems tract models. In: Wilgus, C.K., Hastings,
B.S., Kendall, C.G.S.C., Posamentier, H., Ross, C.A. & Van Wagoner,
J.C. (eds) Sea Level Changes – An Integrated Approach. SEPM, Special
Publications, 42, 125–154.
Pugh, D.T. 1987. Tides, Surges and Mean Sea-Level. Wiley. Chichester.
Rattey, R.P. & Hayward, A.B. 1993. Sequence stratigraphy of a failed rift
system: The Middle Jurassic to Early Cretaceous basin evolution of the
Central and Northern North Sea. In: Parker, J.R. (ed.) Petroleum Geology
of Northwest Europe: Proceedings of the 4th Conference. Geological
Society, London, 4, 215–249.
Ravnås, R. & Bondevik, K. 1997. Architecture and controls on Bathonian–
Kimmeridgian shallow-marine synrift wedges of the Oseberg–Brage area,
northern North Sea. Basin Research, 9, 197–226.
Ravnås, R., Nøttvedt, A., Steel, R.J. & Windelstad, J. 2000. Syn-rift sedimentary architectures in the Northern North Sea. In: Nøttvedt, A. (ed.)
Dynamics of the Norwegian Margin. Geological Society, London, Special
Publications, 167, 133–177.
Raynal, O., Bouchette, F., Certain, R. et al. 2009. Control of alongshoreoriented sand spits on the dynamics of a wave-dominated coastal system
(Holocene deposits, northern Gulf of Lions, France). Marine Geology,
264, 242–257.
Reineck, H.-E. & Singh, I.B. 1973. Depositional Sedimentary Environments.
Springer, Berlin.
Reineck, H.-E. & Wunderlich, F. 1968. Classification and origin of flaser and
lentincular bedding. Sedimentology, 11, 99–104.
Roberts, A.M., Yielding, G. & Badley, M.E. 1990a. A kinematic model
for the orthogonal opening of the late Jurassic North Sea rift system,
Denmark-Mid Norway. In: Blundell, D.J. & Gibbs, A.D. (eds) Tectonic
Evolution of the North Sea Rifts. Oxford Science, Oxford, 181–199.
Serra, O. & Serra, K. 2003. Well Logging and Geology. Editions Serralog,
Méry Corbon, France.
Sixsmith, P.J., Hampson, G.J., Gupta, S., Johnson, H.D. & Fofana, J.F. 2008.
Facies architecture of a net transgressive sandstone reservoir analog:
The Cretaceous Hosta Tongue, New Mexico. American Association of
Petroleum Geologists Bulletin, 92, 513–547.
Steel, R.J. 1993. Triassic–Jurassic megasequence stratigraphy in the Northern
North Sea: Rift to post-rift evolution. In: Parker, J.R. (ed.) Petroleum
Geology of Northwest Europe: Proceedings of the 4th Conference.
Geological Society, London, 4, 299–315.
Stewart, D.J., Schwander, M. & Bolle, L. 1995. Jurassic depositional systems of the horda platform, Norwegian north sea: Practical consequences
of applying sequence stratigraphic models. In: Steel, R.J., Felt, V.L.,
Johannessen, E.P. & Mathieu, C. (eds) Norwegian Petroleum Society,
Special Publications, 5, 291–323.
Swenson, J.B., Paola, C., Pratson, L.F., Voller, V.R. & Murray, A.B. 2005.
Fluvial and marine controls on combined subaerial and subaqueous delta
progradation: Morphodynamic modeling of compound-clinoform development. Journal of Geophysical Research, 110, F02013.
Ta, T.K.O., Nguyen, V.L., Tateishi, M., Kobayashi, I., Saito, Y. &
Nakamura, T. 2002. Sediment facies and Late Holocene progradation of
the Mekong River Delta in Bentre Province, southern Vietnam: An example of evolution from a tide-dominated to a tide- and wave-dominated
delta. Sedimentary Geology, 152, 313–325.
Tanabe, S., Saito, Y., Lan Vu, Q., Hanebuth, T.J.J., Lan Ngo, Q. & Kitamura,
A. 2006. Holocene evolution of the Song Hong (Red River) delta system,
northern Vietnam. Sedimentary Geology, 187, 29–61.
Underhill, J.R. & Partington, M.A. 1993. Jurassic thermal doming and deflation
in the North Sea: Implications of the sequence stratigraphic evidence. In:
Parker, J.R. (ed.) Petroleum Geology of Northwest Europe: Proceedings of
the 4th Conference. Geological Society, London, 4, 337–345.
Vakarelov, B.K., Ainsworth, R.B. & MacEachern, J.A. 2012. Recognition
of wave-dominated, tide-influenced shoreline systems in the rock record:
Variations from a microtidal shoreline model. Sedimentary Geology, 279,
23–41.
Van Den Berg, J.H., Van Gelder, A. & Mastbergen, D.R. 2002. The importance of breaching as a mechanism of subaqueous slope failure in fine
sand. Sedimentology, 49, 81–95.
Van Wagoner, J.C., Mitchum, R.M., Campion, K.M. & Rahmanian, V.D.
1990. Siliciclastic Sequence Stratigraphy in Well Logs, Cores and
Outcrops: Concepts for High-Resolution Correlation of Time and Facies.
American Association of Petroleum Geologists, Methods in Exploration, 7.
Visser, M.J. 1980. Neap-spring cycles reflected in Holocene subtidal largescale bedform deposits: A preliminary note. Geology, 8, 543.
Vollset, J. & Doré, A.G. (eds). 1984. A Revised Triassic and Jurassic
Lithostratigraphic Nomenclature for the Norwegian North Sea.
Norwegian Petroleum Directorate, Bulletin, 3.
Walker, R.G. 1984. Shelf and shallow marine sands. In: Walker, R.G. (ed.)
Facies Models, 2nd edn. Geological Association of Canada, St John’s,
Newfoundland, 141–170.
Whitaker, M.F. 1984. The usage of palynology in definition of Troll Field
geology. Paper presented at the 6th Offshore Northern Seas Conference
and Exhibition, Norsk Petroleumsforening.
Willis, B.J., Bhattacharya, J.P., Gabel, S.L. & White, C.D. 1999. Architecture
of a tide-influenced river delta in the Frontier Formation of central
Wyoming, USA. Sedimentology, 46, 667–688.
Ziegler, P.A. 1990. Geological Atlas of Western and Central Europe, 2nd
edn. Geological Society for Shell Internationale Petroleum, The Hague.
Received 12 June 2012; revised typescript accepted 17 March 2013.